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	$128.59	9.735%	$141.1082	$141.11	$141.10	$141.10
Purchase #2	$33.96	10.559%	$37.5458	$37.55	$37.55	$37.50
Purchase #3	$105.49	5.274%	$111.0535	$111.05	$111.05	$111.10
Purchase #4	$89.86	4.324%	$93.7455	$93.75	$93.75	$93.70
Purchase #5	$150.59	7.573%	$161.9942	$161.99	$162.00	$162.00
Purchase #6	$106.52	13.340%	$120.7298	$120.73	$120.75	$120.70
Purchase #7	$6.90	3.713%	$7.1562	$7.16	$7.15	$7.20
7 purchase totals =	$621.91		$673.3332	$673.34	$673.35	$673.30