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	$30.80	6.717%	$32.8688	$32.87	$32.85	$32.90
Purchase #2	$161.93	4.134%	$168.6242	$168.62	$168.60	$168.60
Purchase #3	$148.87	7.731%	$160.3791	$160.38	$160.40	$160.40
Purchase #4	$103.61	3.199%	$106.9245	$106.92	$106.90	$106.90
Purchase #5	$144.43	7.817%	$155.7201	$155.72	$155.70	$155.70
Purchase #6	$11.69	6.130%	$12.4066	$12.41	$12.40	$12.40
Purchase #7	$199.33	5.145%	$209.5855	$209.59	$209.60	$209.60
7 purchase totals =	$800.66		$846.5088	$846.51	$846.45	$846.50