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	$53.58	10.365%	$59.1336	$59.13	$59.15	$59.10
Purchase #2	$55.86	6.561%	$59.525	$59.53	$59.55	$59.50
Purchase #3	$28.86	11.104%	$32.0646	$32.06	$32.05	$32.10
Purchase #4	$101.53	11.872%	$113.5836	$113.58	$113.60	$113.60
Purchase #5	$123.66	13.352%	$140.1711	$140.17	$140.15	$140.20
Purchase #6	$198.88	11.376%	$221.5046	$221.50	$221.50	$221.50
Purchase #7	$31.79	8.750%	$34.5716	$34.57	$34.55	$34.60
7 purchase totals =	$594.16		$660.5541	$660.54	$660.55	$660.60