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	$42.75	7.355%	$45.8943	$45.89	$45.90	$45.90
Purchase #2	$169.93	3.688%	$176.197	$176.20	$176.20	$176.20
Purchase #3	$149.55	4.412%	$156.1481	$156.15	$156.15	$156.10
Purchase #4	$16.45	13.326%	$18.6421	$18.64	$18.65	$18.60
Purchase #5	$11.87	13.255%	$13.4434	$13.44	$13.45	$13.40
Purchase #6	$54.57	11.820%	$61.0202	$61.02	$61.00	$61.00
Purchase #7	$126.77	13.691%	$144.1261	$144.13	$144.15	$144.10
7 purchase totals =	$571.89		$615.4712	$615.47	$615.50	$615.30