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	$22.94	5.552%	$24.2136	$24.21	$24.20	$24.20
Purchase #2	$239.69	6.185%	$254.5148	$254.51	$254.50	$254.50
Purchase #3	$32.93	13.199%	$37.2764	$37.28	$37.30	$37.30
Purchase #4	$101.61	10.661%	$112.4426	$112.44	$112.45	$112.40
Purchase #5	$38.74	9.761%	$42.5214	$42.52	$42.50	$42.50
Purchase #6	$130.81	11.778%	$146.2168	$146.22	$146.20	$146.20
Purchase #7	$171.67	10.735%	$190.0988	$190.10	$190.10	$190.10
7 purchase totals =	$738.39		$807.2844	$807.28	$807.25	$807.20