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	$236.69	12.761%	$266.894	$266.89	$266.90	$266.90
Purchase #2	$195.97	4.306%	$204.4085	$204.41	$204.40	$204.40
Purchase #3	$97.77	13.312%	$110.7851	$110.79	$110.80	$110.80
Purchase #4	$208.78	6.803%	$222.9833	$222.98	$223.00	$223.00
Purchase #5	$176.95	7.628%	$190.4477	$190.45	$190.45	$190.40
Purchase #6	$162.78	6.223%	$172.9098	$172.91	$172.90	$172.90
Purchase #7	$89.62	11.448%	$99.8797	$99.88	$99.90	$99.90
7 purchase totals =	$1,168.56		$1,268.3081	$1,268.31	$1,268.35	$1,268.30