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	$134.95	5.113%	$141.85	$141.85	$141.85	$141.90
Purchase #2	$100.47	7.108%	$107.6114	$107.61	$107.60	$107.60
Purchase #3	$170.79	10.601%	$188.8954	$188.90	$188.90	$188.90
Purchase #4	$107.82	11.505%	$120.2247	$120.22	$120.20	$120.20
Purchase #5	$106.36	13.342%	$120.5506	$120.55	$120.55	$120.60
Purchase #6	$40.33	5.428%	$42.5191	$42.52	$42.50	$42.50
Purchase #7	$146.98	9.708%	$161.2488	$161.25	$161.25	$161.20
7 purchase totals =	$807.70		$882.9000	$882.90	$882.85	$882.90