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	$37.43	4.620%	$39.1593	$39.16	$39.15	$39.20
Purchase #2	$249.31	12.503%	$280.4812	$280.48	$280.50	$280.50
Purchase #3	$131.63	11.302%	$146.5068	$146.51	$146.50	$146.50
Purchase #4	$155.79	3.207%	$160.7862	$160.79	$160.80	$160.80
Purchase #5	$116.63	10.122%	$128.4353	$128.44	$128.45	$128.40
Purchase #6	$244.32	8.156%	$264.2467	$264.25	$264.25	$264.20
Purchase #7	$50.28	7.535%	$54.0686	$54.07	$54.05	$54.10
7 purchase totals =	$985.39		$1,073.6841	$1,073.70	$1,073.70	$1,073.70