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	$171.58	11.413%	$191.1624	$191.16	$191.15	$191.20
Purchase #2	$148.36	10.770%	$164.3384	$164.34	$164.35	$164.30
Purchase #3	$95.72	10.588%	$105.8548	$105.85	$105.85	$105.90
Purchase #4	$135.60	6.486%	$144.395	$144.40	$144.40	$144.40
Purchase #5	$106.80	8.676%	$116.066	$116.07	$116.05	$116.10
Purchase #6	$131.62	12.725%	$148.3686	$148.37	$148.35	$148.40
Purchase #7	$48.54	3.457%	$50.218	$50.22	$50.20	$50.20
7 purchase totals =	$838.22		$920.4032	$920.41	$920.35	$920.50