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	$142.39	12.328%	$159.9438	$159.94	$159.95	$159.90
Purchase #2	$51.84	4.413%	$54.1277	$54.13	$54.15	$54.10
Purchase #3	$30.31	8.715%	$32.9515	$32.95	$32.95	$33.00
Purchase #4	$149.41	4.193%	$155.6748	$155.67	$155.65	$155.70
Purchase #5	$11.81	13.775%	$13.4368	$13.44	$13.45	$13.40
Purchase #6	$39.98	8.859%	$43.5218	$43.52	$43.50	$43.50
Purchase #7	$171.83	7.851%	$185.3204	$185.32	$185.30	$185.30
7 purchase totals =	$597.57		$644.9768	$644.97	$644.95	$644.90