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	$31.44	12.129%	$35.2534	$35.25	$35.25	$35.30
Purchase #2	$98.63	11.659%	$110.1293	$110.13	$110.15	$110.10
Purchase #3	$192.26	6.377%	$204.5204	$204.52	$204.50	$204.50
Purchase #4	$6.46	5.441%	$6.8115	$6.81	$6.80	$6.80
Purchase #5	$107.37	3.414%	$111.0356	$111.04	$111.05	$111.00
Purchase #6	$42.66	3.315%	$44.0742	$44.07	$44.05	$44.10
Purchase #7	$17.78	13.746%	$20.224	$20.22	$20.20	$20.20
7 purchase totals =	$496.60		$532.0484	$532.04	$532.00	$532.00