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	$57.63	4.198%	$60.0493	$60.05	$60.05	$60.00
Purchase #2	$209.41	6.525%	$223.074	$223.07	$223.05	$223.10
Purchase #3	$71.41	9.574%	$78.2468	$78.25	$78.25	$78.20
Purchase #4	$53.25	12.143%	$59.7161	$59.72	$59.70	$59.70
Purchase #5	$87.40	3.714%	$90.646	$90.65	$90.65	$90.60
Purchase #6	$14.53	3.374%	$15.0202	$15.02	$15.00	$15.00
Purchase #7	$142.49	10.669%	$157.6923	$157.69	$157.70	$157.70
7 purchase totals =	$636.12		$684.4447	$684.45	$684.40	$684.30