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	$139.59	5.865%	$147.777	$147.78	$147.80	$147.80
Purchase #2	$37.53	8.776%	$40.8236	$40.82	$40.80	$40.80
Purchase #3	$138.26	9.199%	$150.9785	$150.98	$151.00	$151.00
Purchase #4	$143.39	6.132%	$152.1827	$152.18	$152.20	$152.20
Purchase #5	$220.98	9.434%	$241.8273	$241.83	$241.85	$241.80
Purchase #6	$31.29	5.202%	$32.9177	$32.92	$32.90	$32.90
Purchase #7	$199.48	4.503%	$208.4626	$208.46	$208.45	$208.50
7 purchase totals =	$910.52		$974.9694	$974.97	$975.00	$975.00