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	$69.48	12.859%	$78.4144	$78.41	$78.40	$78.40
Purchase #2	$94.80	5.302%	$99.8263	$99.83	$99.85	$99.80
Purchase #3	$78.40	12.797%	$88.4328	$88.43	$88.45	$88.40
Purchase #4	$14.45	8.842%	$15.7277	$15.73	$15.75	$15.70
Purchase #5	$47.50	3.419%	$49.124	$49.12	$49.10	$49.10
Purchase #6	$111.41	13.778%	$126.7601	$126.76	$126.75	$126.80
Purchase #7	$144.28	6.673%	$153.9078	$153.91	$153.90	$153.90
7 purchase totals =	$560.32		$612.1931	$612.19	$612.20	$612.10