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	$32.51	3.870%	$33.7681	$33.77	$33.75	$33.80
Purchase #2	$149.85	8.690%	$162.872	$162.87	$162.85	$162.90
Purchase #3	$100.86	5.731%	$106.6403	$106.64	$106.65	$106.60
Purchase #4	$89.29	13.650%	$101.4781	$101.48	$101.50	$101.50
Purchase #5	$108.55	4.276%	$113.1916	$113.19	$113.20	$113.20
Purchase #6	$99.26	10.562%	$109.7438	$109.74	$109.75	$109.70
Purchase #7	$106.63	4.157%	$111.0626	$111.06	$111.05	$111.10
7 purchase totals =	$686.95		$738.7565	$738.75	$738.75	$738.80