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	$112.33	3.539%	$116.3054	$116.31	$116.30	$116.30
Purchase #2	$32.72	9.763%	$35.9145	$35.91	$35.90	$35.90
Purchase #3	$52.68	4.106%	$54.843	$54.84	$54.85	$54.80
Purchase #4	$175.64	11.370%	$195.6103	$195.61	$195.60	$195.60
Purchase #5	$192.76	13.846%	$219.4495	$219.45	$219.45	$219.40
Purchase #6	$44.50	7.523%	$47.8477	$47.85	$47.85	$47.80
Purchase #7	$215.98	13.405%	$244.9321	$244.93	$244.95	$244.90
7 purchase totals =	$826.61		$914.9025	$914.90	$914.90	$914.70