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	$30.81	6.594%	$32.8416	$32.84	$32.85	$32.80
Purchase #2	$52.32	13.425%	$59.344	$59.34	$59.35	$59.30
Purchase #3	$50.91	4.248%	$53.0727	$53.07	$53.05	$53.10
Purchase #4	$28.71	13.700%	$32.6433	$32.64	$32.65	$32.60
Purchase #5	$143.36	3.517%	$148.402	$148.40	$148.40	$148.40
Purchase #6	$139.38	6.781%	$148.8314	$148.83	$148.85	$148.80
Purchase #7	$77.81	4.328%	$81.1776	$81.18	$81.20	$81.20
7 purchase totals =	$523.30		$556.3126	$556.30	$556.35	$556.20