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	$82.40	3.193%	$85.031	$85.03	$85.05	$85.00
Purchase #2	$157.89	10.442%	$174.3769	$174.38	$174.40	$174.40
Purchase #3	$134.78	5.197%	$141.7845	$141.78	$141.80	$141.80
Purchase #4	$151.51	9.195%	$165.4413	$165.44	$165.45	$165.40
Purchase #5	$16.92	3.331%	$17.4836	$17.48	$17.50	$17.50
Purchase #6	$31.77	13.631%	$36.1006	$36.10	$36.10	$36.10
Purchase #7	$33.51	11.650%	$37.4139	$37.41	$37.40	$37.40
7 purchase totals =	$608.78		$657.6318	$657.62	$657.70	$657.60