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	$66.55	6.228%	$70.6947	$70.69	$70.70	$70.70
Purchase #2	$41.99	4.390%	$43.8334	$43.83	$43.85	$43.80
Purchase #3	$140.33	10.605%	$155.212	$155.21	$155.20	$155.20
Purchase #4	$59.35	3.590%	$61.4807	$61.48	$61.50	$61.50
Purchase #5	$153.38	4.409%	$160.1425	$160.14	$160.15	$160.10
Purchase #6	$11.63	11.811%	$13.0036	$13.00	$13.00	$13.00
Purchase #7	$83.47	8.868%	$90.8721	$90.87	$90.85	$90.90
7 purchase totals =	$556.70		$595.2390	$595.22	$595.25	$595.20