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	$53.33	8.490%	$57.8577	$57.86	$57.85	$57.90
Purchase #2	$173.33	6.861%	$185.2222	$185.22	$185.20	$185.20
Purchase #3	$223.36	12.448%	$251.1639	$251.16	$251.15	$251.20
Purchase #4	$108.77	10.255%	$119.9244	$119.92	$119.90	$119.90
Purchase #5	$20.66	10.493%	$22.8279	$22.83	$22.85	$22.80
Purchase #6	$40.97	4.681%	$42.8878	$42.89	$42.90	$42.90
Purchase #7	$22.78	13.192%	$25.7851	$25.79	$25.80	$25.80
7 purchase totals =	$643.20		$705.6690	$705.67	$705.65	$705.70