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	$101.40	10.359%	$111.904	$111.90	$111.90	$111.90
Purchase #2	$174.57	9.614%	$191.3532	$191.35	$191.35	$191.40
Purchase #3	$239.28	3.841%	$248.4707	$248.47	$248.45	$248.50
Purchase #4	$132.77	11.654%	$148.243	$148.24	$148.25	$148.20
Purchase #5	$58.81	10.644%	$65.0697	$65.07	$65.05	$65.10
Purchase #6	$91.71	10.699%	$101.5221	$101.52	$101.50	$101.50
Purchase #7	$67.72	12.243%	$76.011	$76.01	$76.00	$76.00
7 purchase totals =	$866.26		$942.5737	$942.56	$942.50	$942.60