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	$89.36	12.109%	$100.1806	$100.18	$100.20	$100.20
Purchase #2	$94.88	9.749%	$104.1299	$104.13	$104.15	$104.10
Purchase #3	$59.79	12.458%	$67.2386	$67.24	$67.25	$67.20
Purchase #4	$126.61	11.760%	$141.4993	$141.50	$141.50	$141.50
Purchase #5	$40.70	11.460%	$45.3642	$45.36	$45.35	$45.40
Purchase #6	$214.52	5.525%	$226.3722	$226.37	$226.35	$226.40
Purchase #7	$161.71	11.150%	$179.7407	$179.74	$179.75	$179.70
7 purchase totals =	$787.57		$864.5255	$864.52	$864.55	$864.50