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	$127.51	8.520%	$138.3739	$138.37	$138.35	$138.40
Purchase #2	$122.79	13.244%	$139.0523	$139.05	$139.05	$139.10
Purchase #3	$28.98	11.306%	$32.2565	$32.26	$32.25	$32.30
Purchase #4	$59.62	3.732%	$61.845	$61.85	$61.85	$61.80
Purchase #5	$165.66	11.860%	$185.3073	$185.31	$185.30	$185.30
Purchase #6	$121.52	13.421%	$137.8292	$137.83	$137.85	$137.80
Purchase #7	$182.90	13.430%	$207.4635	$207.46	$207.45	$207.50
7 purchase totals =	$808.98		$902.1277	$902.13	$902.10	$902.20