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	$47.75	13.534%	$54.2125	$54.21	$54.20	$54.20
Purchase #2	$41.45	9.715%	$45.4769	$45.48	$45.50	$45.50
Purchase #3	$232.82	11.344%	$259.2311	$259.23	$259.25	$259.20
Purchase #4	$88.65	12.531%	$99.7587	$99.76	$99.75	$99.80
Purchase #5	$229.70	12.587%	$258.6123	$258.61	$258.60	$258.60
Purchase #6	$161.31	7.493%	$173.397	$173.40	$173.40	$173.40
Purchase #7	$104.72	6.199%	$111.2116	$111.21	$111.20	$111.20
7 purchase totals =	$906.40		$1,001.9001	$1,001.90	$1,001.90	$1,001.90