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	$28.54	13.287%	$32.3321	$32.33	$32.35	$32.30
Purchase #2	$106.58	7.801%	$114.8943	$114.89	$114.90	$114.90
Purchase #3	$138.35	13.520%	$157.0549	$157.05	$157.05	$157.10
Purchase #4	$195.33	12.642%	$220.0236	$220.02	$220.00	$220.00
Purchase #5	$79.54	4.816%	$83.3706	$83.37	$83.35	$83.40
Purchase #6	$110.93	11.810%	$124.0308	$124.03	$124.05	$124.00
Purchase #7	$32.33	6.774%	$34.52	$34.52	$34.50	$34.50
7 purchase totals =	$691.60		$766.2263	$766.21	$766.20	$766.20