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	$99.73	4.130%	$103.8488	$103.85	$103.85	$103.80
Purchase #2	$204.98	7.764%	$220.8946	$220.89	$220.90	$220.90
Purchase #3	$157.48	6.818%	$168.217	$168.22	$168.20	$168.20
Purchase #4	$106.34	5.479%	$112.1664	$112.17	$112.15	$112.20
Purchase #5	$132.28	10.753%	$146.5041	$146.50	$146.50	$146.50
Purchase #6	$118.84	9.262%	$129.847	$129.85	$129.85	$129.80
Purchase #7	$83.98	6.298%	$89.2691	$89.27	$89.25	$89.30
7 purchase totals =	$903.63		$970.7470	$970.75	$970.70	$970.70