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	$204.31	10.217%	$225.1844	$225.18	$225.20	$225.20
Purchase #2	$235.77	11.369%	$262.5747	$262.57	$262.55	$262.60
Purchase #3	$182.95	11.283%	$203.5922	$203.59	$203.60	$203.60
Purchase #4	$36.88	10.218%	$40.6484	$40.65	$40.65	$40.60
Purchase #5	$42.46	11.385%	$47.2941	$47.29	$47.30	$47.30
Purchase #6	$243.62	3.398%	$251.8982	$251.90	$251.90	$251.90
Purchase #7	$54.89	13.486%	$62.2925	$62.29	$62.30	$62.30
7 purchase totals =	$1,000.88		$1,093.4845	$1,093.47	$1,093.50	$1,093.50