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	$88.25	13.841%	$100.4647	$100.46	$100.45	$100.50
Purchase #2	$34.25	7.218%	$36.7222	$36.72	$36.70	$36.70
Purchase #3	$49.65	11.167%	$55.1944	$55.19	$55.20	$55.20
Purchase #4	$93.37	5.558%	$98.5595	$98.56	$98.55	$98.60
Purchase #5	$49.52	6.169%	$52.5749	$52.57	$52.55	$52.60
Purchase #6	$75.71	9.862%	$83.1765	$83.18	$83.20	$83.20
Purchase #7	$109.85	8.773%	$119.4871	$119.49	$119.50	$119.50
7 purchase totals =	$500.60		$546.1793	$546.17	$546.15	$546.30