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	$188.83	7.528%	$203.0451	$203.05	$203.05	$203.00
Purchase #2	$18.33	9.482%	$20.0681	$20.07	$20.05	$20.10
Purchase #3	$203.88	7.160%	$218.4778	$218.48	$218.50	$218.50
Purchase #4	$59.28	7.188%	$63.541	$63.54	$63.55	$63.50
Purchase #5	$45.38	5.404%	$47.8323	$47.83	$47.85	$47.80
Purchase #6	$223.77	3.198%	$230.9262	$230.93	$230.95	$230.90
Purchase #7	$61.69	9.366%	$67.4679	$67.47	$67.45	$67.50
7 purchase totals =	$801.16		$851.3584	$851.37	$851.40	$851.30