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	$79.55	13.362%	$90.1795	$90.18	$90.20	$90.20
Purchase #2	$188.49	3.763%	$195.5829	$195.58	$195.60	$195.60
Purchase #3	$247.57	11.374%	$275.7286	$275.73	$275.75	$275.70
Purchase #4	$7.82	11.522%	$8.721	$8.72	$8.70	$8.70
Purchase #5	$119.53	10.345%	$131.8954	$131.90	$131.90	$131.90
Purchase #6	$15.82	9.581%	$17.3357	$17.34	$17.35	$17.30
Purchase #7	$243.79	8.475%	$264.4512	$264.45	$264.45	$264.50
7 purchase totals =	$902.57		$983.8943	$983.90	$983.95	$983.90