Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$235.95	6.511%	$251.3127	$251.31	$251.30	$251.30
Purchase #2	$188.92	10.503%	$208.7623	$208.76	$208.75	$208.80
Purchase #3	$101.76	7.246%	$109.1335	$109.13	$109.15	$109.10
Purchase #4	$145.90	12.510%	$164.1521	$164.15	$164.15	$164.20
Purchase #5	$57.52	5.366%	$60.6065	$60.61	$60.60	$60.60
Purchase #6	$191.86	3.740%	$199.0356	$199.04	$199.05	$199.00
Purchase #7	$231.29	13.374%	$262.2227	$262.22	$262.20	$262.20
7 purchase totals =	$1,153.20		$1,255.2254	$1,255.22	$1,255.20	$1,255.20