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	$244.59	13.220%	$276.9248	$276.92	$276.90	$276.90
Purchase #2	$16.65	5.144%	$17.5065	$17.51	$17.50	$17.50
Purchase #3	$180.76	10.582%	$199.888	$199.89	$199.90	$199.90
Purchase #4	$20.50	3.448%	$21.2068	$21.21	$21.20	$21.20
Purchase #5	$98.56	13.124%	$111.495	$111.50	$111.50	$111.50
Purchase #6	$149.35	8.126%	$161.4862	$161.49	$161.50	$161.50
Purchase #7	$123.69	13.317%	$140.1618	$140.16	$140.15	$140.20
7 purchase totals =	$834.10		$928.6691	$928.68	$928.65	$928.70