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	$36.87	9.362%	$40.3218	$40.32	$40.30	$40.30
Purchase #2	$81.96	7.224%	$87.8808	$87.88	$87.90	$87.90
Purchase #3	$65.30	11.652%	$72.9088	$72.91	$72.90	$72.90
Purchase #4	$203.89	11.500%	$227.3374	$227.34	$227.35	$227.30
Purchase #5	$87.43	9.553%	$95.7822	$95.78	$95.80	$95.80
Purchase #6	$108.90	6.499%	$115.9774	$115.98	$116.00	$116.00
Purchase #7	$58.71	5.324%	$61.8357	$61.84	$61.85	$61.80
7 purchase totals =	$643.06		$702.0441	$702.05	$702.10	$702.00