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	$159.98	6.676%	$170.6603	$170.66	$170.65	$170.70
Purchase #2	$195.89	6.785%	$209.1811	$209.18	$209.20	$209.20
Purchase #3	$113.59	13.368%	$128.7747	$128.77	$128.75	$128.80
Purchase #4	$130.45	6.472%	$138.8927	$138.89	$138.90	$138.90
Purchase #5	$55.75	5.174%	$58.6345	$58.63	$58.65	$58.60
Purchase #6	$76.54	11.356%	$85.2319	$85.23	$85.25	$85.20
Purchase #7	$40.82	11.574%	$45.5445	$45.54	$45.55	$45.50
7 purchase totals =	$773.02		$836.9197	$836.90	$836.95	$836.90