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	$64.75	8.302%	$70.1255	$70.13	$70.15	$70.10
Purchase #2	$37.61	8.388%	$40.7647	$40.76	$40.75	$40.80
Purchase #3	$89.59	8.619%	$97.3118	$97.31	$97.30	$97.30
Purchase #4	$34.54	13.218%	$39.1055	$39.11	$39.10	$39.10
Purchase #5	$79.46	5.488%	$83.8208	$83.82	$83.80	$83.80
Purchase #6	$231.43	6.651%	$246.8224	$246.82	$246.80	$246.80
Purchase #7	$83.77	6.593%	$89.293	$89.29	$89.30	$89.30
7 purchase totals =	$621.15		$667.2437	$667.24	$667.20	$667.20