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	$113.62	4.259%	$118.4591	$118.46	$118.45	$118.50
Purchase #2	$137.78	13.472%	$156.3417	$156.34	$156.35	$156.30
Purchase #3	$80.39	10.476%	$88.8117	$88.81	$88.80	$88.80
Purchase #4	$140.66	13.443%	$159.5689	$159.57	$159.55	$159.60
Purchase #5	$12.50	6.542%	$13.3178	$13.32	$13.30	$13.30
Purchase #6	$130.33	11.211%	$144.9413	$144.94	$144.95	$144.90
Purchase #7	$203.29	6.818%	$217.1503	$217.15	$217.15	$217.20
7 purchase totals =	$818.57		$898.5908	$898.59	$898.55	$898.60