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	$29.37	13.420%	$33.3115	$33.31	$33.30	$33.30
Purchase #2	$162.70	10.167%	$179.2417	$179.24	$179.25	$179.20
Purchase #3	$109.78	12.268%	$123.2478	$123.25	$123.25	$123.20
Purchase #4	$120.83	13.561%	$137.2158	$137.22	$137.20	$137.20
Purchase #5	$229.37	8.412%	$248.6646	$248.66	$248.65	$248.70
Purchase #6	$138.28	5.737%	$146.2131	$146.21	$146.20	$146.20
Purchase #7	$203.50	7.637%	$219.0413	$219.04	$219.05	$219.00
7 purchase totals =	$993.83		$1,086.9358	$1,086.93	$1,086.90	$1,086.80