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	$85.65	3.601%	$88.7343	$88.73	$88.75	$88.70
Purchase #2	$167.37	13.562%	$190.0687	$190.07	$190.05	$190.10
Purchase #3	$38.36	6.518%	$40.8603	$40.86	$40.85	$40.90
Purchase #4	$34.45	7.462%	$37.0207	$37.02	$37.00	$37.00
Purchase #5	$22.28	10.843%	$24.6958	$24.70	$24.70	$24.70
Purchase #6	$77.72	10.126%	$85.5899	$85.59	$85.60	$85.60
Purchase #7	$126.35	12.217%	$141.7862	$141.79	$141.80	$141.80
7 purchase totals =	$552.18		$608.7559	$608.76	$608.75	$608.80