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	$185.54	12.374%	$208.4987	$208.50	$208.50	$208.50
Purchase #2	$69.40	13.540%	$78.7968	$78.80	$78.80	$78.80
Purchase #3	$131.98	7.302%	$141.6172	$141.62	$141.60	$141.60
Purchase #4	$117.29	12.437%	$131.8774	$131.88	$131.90	$131.90
Purchase #5	$73.47	13.517%	$83.4009	$83.40	$83.40	$83.40
Purchase #6	$82.34	8.338%	$89.2055	$89.21	$89.20	$89.20
Purchase #7	$235.80	5.398%	$248.5285	$248.53	$248.55	$248.50
7 purchase totals =	$895.82		$981.9250	$981.94	$981.95	$981.90