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	$153.98	11.799%	$172.1481	$172.15	$172.15	$172.10
Purchase #2	$79.52	9.300%	$86.9154	$86.92	$86.90	$86.90
Purchase #3	$93.67	10.421%	$103.4314	$103.43	$103.45	$103.40
Purchase #4	$36.75	10.307%	$40.5378	$40.54	$40.55	$40.50
Purchase #5	$133.39	5.535%	$140.7731	$140.77	$140.75	$140.80
Purchase #6	$10.79	6.848%	$11.5289	$11.53	$11.55	$11.50
Purchase #7	$187.80	6.456%	$199.9244	$199.92	$199.90	$199.90
7 purchase totals =	$695.90		$755.2591	$755.26	$755.25	$755.10