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	$209.33	5.683%	$221.2262	$221.23	$221.25	$221.20
Purchase #2	$136.34	11.249%	$151.6769	$151.68	$151.70	$151.70
Purchase #3	$125.89	9.319%	$137.6217	$137.62	$137.60	$137.60
Purchase #4	$98.42	12.831%	$111.0483	$111.05	$111.05	$111.00
Purchase #5	$161.89	11.485%	$180.4831	$180.48	$180.50	$180.50
Purchase #6	$245.57	3.776%	$254.8427	$254.84	$254.85	$254.80
Purchase #7	$52.82	7.758%	$56.9178	$56.92	$56.90	$56.90
7 purchase totals =	$1,030.26		$1,113.8167	$1,113.82	$1,113.85	$1,113.70