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	$250.48	11.810%	$280.0617	$280.06	$280.05	$280.10
Purchase #2	$199.72	9.847%	$219.3864	$219.39	$219.40	$219.40
Purchase #3	$146.53	13.544%	$166.376	$166.38	$166.40	$166.40
Purchase #4	$134.38	12.479%	$151.1493	$151.15	$151.15	$151.10
Purchase #5	$243.43	5.532%	$256.8965	$256.90	$256.90	$256.90
Purchase #6	$191.89	9.512%	$210.1426	$210.14	$210.15	$210.10
Purchase #7	$126.52	3.449%	$130.8837	$130.88	$130.90	$130.90
7 purchase totals =	$1,292.95		$1,414.8962	$1,414.90	$1,414.95	$1,414.90