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	$38.31	5.790%	$40.5281	$40.53	$40.55	$40.50
Purchase #2	$66.46	10.294%	$73.3014	$73.30	$73.30	$73.30
Purchase #3	$16.50	4.306%	$17.2105	$17.21	$17.20	$17.20
Purchase #4	$66.68	5.375%	$70.2641	$70.26	$70.25	$70.30
Purchase #5	$40.91	10.706%	$45.2898	$45.29	$45.30	$45.30
Purchase #6	$53.86	10.741%	$59.6451	$59.65	$59.65	$59.60
Purchase #7	$73.51	3.600%	$76.1564	$76.16	$76.15	$76.20
7 purchase totals =	$356.23		$382.3954	$382.40	$382.40	$382.40