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	$127.52	12.257%	$143.1501	$143.15	$143.15	$143.20
Purchase #2	$219.68	7.311%	$235.7408	$235.74	$235.75	$235.70
Purchase #3	$234.37	6.740%	$250.1665	$250.17	$250.15	$250.20
Purchase #4	$187.94	6.760%	$200.6447	$200.64	$200.65	$200.60
Purchase #5	$235.89	8.685%	$256.377	$256.38	$256.40	$256.40
Purchase #6	$111.46	9.118%	$121.6229	$121.62	$121.60	$121.60
Purchase #7	$117.54	11.668%	$131.2546	$131.25	$131.25	$131.30
7 purchase totals =	$1,234.40		$1,338.9566	$1,338.95	$1,338.95	$1,339.00