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	$20.25	7.204%	$21.7088	$21.71	$21.70	$21.70
Purchase #2	$243.91	8.802%	$265.379	$265.38	$265.40	$265.40
Purchase #3	$91.32	9.610%	$100.0959	$100.10	$100.10	$100.10
Purchase #4	$114.83	13.715%	$130.5789	$130.58	$130.60	$130.60
Purchase #5	$14.95	4.516%	$15.6251	$15.63	$15.65	$15.60
Purchase #6	$67.31	11.266%	$74.8931	$74.89	$74.90	$74.90
Purchase #7	$17.74	13.691%	$20.1688	$20.17	$20.15	$20.20
7 purchase totals =	$570.31		$628.4496	$628.46	$628.50	$628.50