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	$119.50	10.703%	$132.2901	$132.29	$132.30	$132.30
Purchase #2	$155.56	6.519%	$165.701	$165.70	$165.70	$165.70
Purchase #3	$111.93	10.288%	$123.4454	$123.45	$123.45	$123.40
Purchase #4	$224.89	7.792%	$242.4134	$242.41	$242.40	$242.40
Purchase #5	$147.25	8.223%	$159.3584	$159.36	$159.35	$159.40
Purchase #6	$221.53	12.142%	$248.4282	$248.43	$248.45	$248.40
Purchase #7	$85.34	10.402%	$94.2171	$94.22	$94.20	$94.20
7 purchase totals =	$1,066.00		$1,165.8536	$1,165.86	$1,165.85	$1,165.80