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	$136.34	9.818%	$149.7259	$149.73	$149.75	$149.70
Purchase #2	$151.88	9.603%	$166.465	$166.47	$166.45	$166.50
Purchase #3	$38.66	11.181%	$42.9826	$42.98	$43.00	$43.00
Purchase #4	$98.32	13.793%	$111.8813	$111.88	$111.90	$111.90
Purchase #5	$71.71	6.208%	$76.1618	$76.16	$76.15	$76.20
Purchase #6	$103.92	7.726%	$111.9489	$111.95	$111.95	$111.90
Purchase #7	$22.98	5.259%	$24.1885	$24.19	$24.20	$24.20
7 purchase totals =	$623.81		$683.3540	$683.36	$683.40	$683.40