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	$199.41	8.399%	$216.1584	$216.16	$216.15	$216.20
Purchase #2	$79.66	10.816%	$88.276	$88.28	$88.30	$88.30
Purchase #3	$169.43	12.171%	$190.0513	$190.05	$190.05	$190.10
Purchase #4	$241.78	7.383%	$259.6306	$259.63	$259.65	$259.60
Purchase #5	$29.87	10.520%	$33.0123	$33.01	$33.00	$33.00
Purchase #6	$152.93	10.422%	$168.8684	$168.87	$168.85	$168.90
Purchase #7	$33.46	11.652%	$37.3588	$37.36	$37.35	$37.40
7 purchase totals =	$906.54		$993.3558	$993.36	$993.35	$993.50