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	$24.32	5.687%	$25.7031	$25.70	$25.70	$25.70
Purchase #2	$91.38	7.389%	$98.1321	$98.13	$98.15	$98.10
Purchase #3	$196.47	13.282%	$222.5651	$222.57	$222.55	$222.60
Purchase #4	$199.61	12.344%	$224.2499	$224.25	$224.25	$224.20
Purchase #5	$25.25	6.391%	$26.8637	$26.86	$26.85	$26.90
Purchase #6	$57.31	7.550%	$61.6369	$61.64	$61.65	$61.60
Purchase #7	$127.62	11.783%	$142.6575	$142.66	$142.65	$142.70
7 purchase totals =	$721.96		$801.8083	$801.81	$801.80	$801.80