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	$101.67	3.217%	$104.9407	$104.94	$104.95	$104.90
Purchase #2	$81.38	10.851%	$90.2105	$90.21	$90.20	$90.20
Purchase #3	$62.39	7.571%	$67.1135	$67.11	$67.10	$67.10
Purchase #4	$163.42	13.291%	$185.1402	$185.14	$185.15	$185.10
Purchase #5	$37.81	8.831%	$41.149	$41.15	$41.15	$41.10
Purchase #6	$57.79	6.748%	$61.6897	$61.69	$61.70	$61.70
Purchase #7	$119.90	8.438%	$130.0172	$130.02	$130.00	$130.00
7 purchase totals =	$624.36		$680.2608	$680.26	$680.25	$680.10