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	$134.94	7.829%	$145.5045	$145.50	$145.50	$145.50
Purchase #2	$36.31	8.308%	$39.3266	$39.33	$39.35	$39.30
Purchase #3	$88.30	12.240%	$99.1079	$99.11	$99.10	$99.10
Purchase #4	$244.76	5.513%	$258.2536	$258.25	$258.25	$258.30
Purchase #5	$81.76	13.833%	$93.0699	$93.07	$93.05	$93.10
Purchase #6	$106.43	12.160%	$119.3719	$119.37	$119.35	$119.40
Purchase #7	$180.38	11.340%	$200.8351	$200.84	$200.85	$200.80
7 purchase totals =	$872.88		$955.4695	$955.47	$955.45	$955.50