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	$7.76	11.446%	$8.6482	$8.65	$8.65	$8.60
Purchase #2	$234.84	13.345%	$266.1794	$266.18	$266.20	$266.20
Purchase #3	$140.67	10.274%	$155.1224	$155.12	$155.10	$155.10
Purchase #4	$37.89	12.330%	$42.5618	$42.56	$42.55	$42.60
Purchase #5	$231.51	11.624%	$258.4207	$258.42	$258.40	$258.40
Purchase #6	$62.64	12.122%	$70.2332	$70.23	$70.25	$70.20
Purchase #7	$32.45	10.644%	$35.904	$35.90	$35.90	$35.90
7 purchase totals =	$747.76		$837.0697	$837.06	$837.05	$837.00