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	$121.70	11.843%	$136.1129	$136.11	$136.10	$136.10
Purchase #2	$125.95	8.827%	$137.0676	$137.07	$137.05	$137.10
Purchase #3	$166.32	7.534%	$178.8505	$178.85	$178.85	$178.90
Purchase #4	$192.27	4.176%	$200.2992	$200.30	$200.30	$200.30
Purchase #5	$232.89	13.125%	$263.4568	$263.46	$263.45	$263.50
Purchase #6	$74.51	6.747%	$79.5372	$79.54	$79.55	$79.50
Purchase #7	$59.51	3.507%	$61.597	$61.60	$61.60	$61.60
7 purchase totals =	$973.15		$1,056.9212	$1,056.93	$1,056.90	$1,057.00