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	$87.40	13.388%	$99.1011	$99.10	$99.10	$99.10
Purchase #2	$38.63	12.373%	$43.4097	$43.41	$43.40	$43.40
Purchase #3	$75.72	6.328%	$80.5116	$80.51	$80.50	$80.50
Purchase #4	$20.51	7.468%	$22.0417	$22.04	$22.05	$22.00
Purchase #5	$236.87	7.599%	$254.8698	$254.87	$254.85	$254.90
Purchase #6	$37.42	4.618%	$39.1481	$39.15	$39.15	$39.10
Purchase #7	$99.31	11.306%	$110.538	$110.54	$110.55	$110.50
7 purchase totals =	$595.86		$649.6200	$649.62	$649.60	$649.50