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	$158.74	8.502%	$172.2361	$172.24	$172.25	$172.20
Purchase #2	$139.50	12.307%	$156.6683	$156.67	$156.65	$156.70
Purchase #3	$40.48	13.332%	$45.8768	$45.88	$45.90	$45.90
Purchase #4	$47.48	13.444%	$53.8632	$53.86	$53.85	$53.90
Purchase #5	$26.92	13.342%	$30.5117	$30.51	$30.50	$30.50
Purchase #6	$97.91	13.602%	$111.2277	$111.23	$111.25	$111.20
Purchase #7	$160.55	13.837%	$182.7653	$182.77	$182.75	$182.80
7 purchase totals =	$671.58		$753.1491	$753.16	$753.15	$753.20