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	$11.73	8.318%	$12.7057	$12.71	$12.70	$12.70
Purchase #2	$165.37	8.759%	$179.8548	$179.85	$179.85	$179.90
Purchase #3	$119.44	5.711%	$126.2612	$126.26	$126.25	$126.30
Purchase #4	$83.66	3.438%	$86.5362	$86.54	$86.55	$86.50
Purchase #5	$113.86	8.301%	$123.3115	$123.31	$123.30	$123.30
Purchase #6	$74.46	11.784%	$83.2344	$83.23	$83.25	$83.20
Purchase #7	$76.89	13.462%	$87.2409	$87.24	$87.25	$87.20
7 purchase totals =	$645.41		$699.1447	$699.14	$699.15	$699.10