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	$106.42	12.637%	$119.8683	$119.87	$119.85	$119.90
Purchase #2	$76.72	9.130%	$83.7245	$83.72	$83.70	$83.70
Purchase #3	$184.82	13.513%	$209.7947	$209.79	$209.80	$209.80
Purchase #4	$45.40	11.643%	$50.6859	$50.69	$50.70	$50.70
Purchase #5	$31.38	4.594%	$32.8216	$32.82	$32.80	$32.80
Purchase #6	$154.63	3.432%	$159.9369	$159.94	$159.95	$159.90
Purchase #7	$77.55	7.561%	$83.4136	$83.41	$83.40	$83.40
7 purchase totals =	$676.92		$740.2455	$740.24	$740.20	$740.20