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	$162.58	4.735%	$170.2782	$170.28	$170.30	$170.30
Purchase #2	$146.87	8.570%	$159.4568	$159.46	$159.45	$159.50
Purchase #3	$128.59	9.351%	$140.6145	$140.61	$140.60	$140.60
Purchase #4	$240.98	10.123%	$265.3744	$265.37	$265.35	$265.40
Purchase #5	$78.94	8.443%	$85.6049	$85.60	$85.60	$85.60
Purchase #6	$230.79	12.635%	$259.9503	$259.95	$259.95	$260.00
Purchase #7	$71.90	7.504%	$77.2954	$77.30	$77.30	$77.30
7 purchase totals =	$1,060.65		$1,158.5745	$1,158.57	$1,158.55	$1,158.70