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	$111.39	10.360%	$122.93	$122.93	$122.95	$122.90
Purchase #2	$223.32	9.413%	$244.3411	$244.34	$244.35	$244.30
Purchase #3	$221.27	11.690%	$247.1365	$247.14	$247.15	$247.10
Purchase #4	$74.56	12.820%	$84.1186	$84.12	$84.10	$84.10
Purchase #5	$40.65	6.770%	$43.402	$43.40	$43.40	$43.40
Purchase #6	$102.81	8.757%	$111.8131	$111.81	$111.80	$111.80
Purchase #7	$169.27	9.685%	$185.6638	$185.66	$185.65	$185.70
7 purchase totals =	$943.27		$1,039.4051	$1,039.40	$1,039.40	$1,039.30