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	$6.79	9.735%	$7.451	$7.45	$7.45	$7.50
Purchase #2	$176.88	8.237%	$191.4496	$191.45	$191.45	$191.40
Purchase #3	$146.77	4.307%	$153.0914	$153.09	$153.10	$153.10
Purchase #4	$187.43	11.499%	$208.9826	$208.98	$209.00	$209.00
Purchase #5	$12.61	6.553%	$13.4363	$13.44	$13.45	$13.40
Purchase #6	$183.72	4.150%	$191.3444	$191.34	$191.35	$191.30
Purchase #7	$30.63	8.871%	$33.3472	$33.35	$33.35	$33.30
7 purchase totals =	$744.83		$799.1025	$799.10	$799.15	$799.00