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	$64.58	9.270%	$70.5666	$70.57	$70.55	$70.60
Purchase #2	$43.71	5.759%	$46.2273	$46.23	$46.25	$46.20
Purchase #3	$244.74	5.535%	$258.2864	$258.29	$258.30	$258.30
Purchase #4	$81.50	13.573%	$92.562	$92.56	$92.55	$92.60
Purchase #5	$85.58	4.120%	$89.1059	$89.11	$89.10	$89.10
Purchase #6	$139.95	13.854%	$159.3387	$159.34	$159.35	$159.30
Purchase #7	$207.32	11.563%	$231.2924	$231.29	$231.30	$231.30
7 purchase totals =	$867.38		$947.3793	$947.39	$947.40	$947.40