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	$32.41	3.872%	$33.6649	$33.66	$33.65	$33.70
Purchase #2	$90.30	12.503%	$101.5902	$101.59	$101.60	$101.60
Purchase #3	$136.30	10.125%	$150.1004	$150.10	$150.10	$150.10
Purchase #4	$62.62	7.811%	$67.5112	$67.51	$67.50	$67.50
Purchase #5	$244.35	12.661%	$275.2872	$275.29	$275.30	$275.30
Purchase #6	$113.49	9.659%	$124.452	$124.45	$124.45	$124.50
Purchase #7	$147.25	8.620%	$159.943	$159.94	$159.95	$159.90
7 purchase totals =	$826.72		$912.5489	$912.54	$912.55	$912.60