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	$17.86	7.252%	$19.1552	$19.16	$19.15	$19.20
Purchase #2	$125.25	11.712%	$139.9193	$139.92	$139.90	$139.90
Purchase #3	$20.77	10.456%	$22.9417	$22.94	$22.95	$22.90
Purchase #4	$147.99	4.410%	$154.5164	$154.52	$154.50	$154.50
Purchase #5	$18.91	8.616%	$20.5393	$20.54	$20.55	$20.50
Purchase #6	$235.30	7.870%	$253.8181	$253.82	$253.80	$253.80
Purchase #7	$90.43	9.551%	$99.067	$99.07	$99.05	$99.10
7 purchase totals =	$656.51		$709.9570	$709.97	$709.90	$709.90