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	$95.30	5.413%	$100.4586	$100.46	$100.45	$100.50
Purchase #2	$146.84	7.453%	$157.784	$157.78	$157.80	$157.80
Purchase #3	$203.36	7.483%	$218.5774	$218.58	$218.60	$218.60
Purchase #4	$45.85	10.361%	$50.6005	$50.60	$50.60	$50.60
Purchase #5	$131.51	7.434%	$141.2865	$141.29	$141.30	$141.30
Purchase #6	$54.51	13.630%	$61.9397	$61.94	$61.95	$61.90
Purchase #7	$139.78	5.733%	$147.7936	$147.79	$147.80	$147.80
7 purchase totals =	$817.15		$878.4403	$878.44	$878.50	$878.50