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	$136.71	9.854%	$150.1814	$150.18	$150.20	$150.20
Purchase #2	$223.55	11.298%	$248.8067	$248.81	$248.80	$248.80
Purchase #3	$145.42	10.420%	$160.5728	$160.57	$160.55	$160.60
Purchase #4	$19.88	6.741%	$21.2201	$21.22	$21.20	$21.20
Purchase #5	$221.43	5.627%	$233.8899	$233.89	$233.90	$233.90
Purchase #6	$118.53	6.149%	$125.8184	$125.82	$125.80	$125.80
Purchase #7	$167.80	8.859%	$182.6654	$182.67	$182.65	$182.70
7 purchase totals =	$1,033.32		$1,123.1547	$1,123.16	$1,123.10	$1,123.20