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	$40.89	3.430%	$42.2925	$42.29	$42.30	$42.30
Purchase #2	$58.80	12.736%	$66.2888	$66.29	$66.30	$66.30
Purchase #3	$104.69	12.409%	$117.681	$117.68	$117.70	$117.70
Purchase #4	$235.69	7.563%	$253.5152	$253.52	$253.50	$253.50
Purchase #5	$91.79	9.310%	$100.3356	$100.34	$100.35	$100.30
Purchase #6	$63.26	12.273%	$71.0239	$71.02	$71.00	$71.00
Purchase #7	$169.29	6.641%	$180.5325	$180.53	$180.55	$180.50
7 purchase totals =	$764.41		$831.6695	$831.67	$831.70	$831.60