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	$200.59	10.235%	$221.1204	$221.12	$221.10	$221.10
Purchase #2	$90.74	10.817%	$100.5553	$100.56	$100.55	$100.60
Purchase #3	$139.76	9.846%	$153.5208	$153.52	$153.50	$153.50
Purchase #4	$15.47	10.772%	$17.1364	$17.14	$17.15	$17.10
Purchase #5	$50.29	12.743%	$56.6985	$56.70	$56.70	$56.70
Purchase #6	$234.85	6.483%	$250.0753	$250.08	$250.10	$250.10
Purchase #7	$6.61	3.854%	$6.8647	$6.86	$6.85	$6.90
7 purchase totals =	$738.31		$805.9714	$805.98	$805.95	$806.00