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	$50.64	6.139%	$53.7488	$53.75	$53.75	$53.70
Purchase #2	$172.25	11.200%	$191.542	$191.54	$191.55	$191.50
Purchase #3	$113.64	3.212%	$117.2901	$117.29	$117.30	$117.30
Purchase #4	$175.34	7.168%	$187.9084	$187.91	$187.90	$187.90
Purchase #5	$11.53	8.175%	$12.4726	$12.47	$12.45	$12.50
Purchase #6	$209.79	12.503%	$236.02	$236.02	$236.00	$236.00
Purchase #7	$68.27	5.367%	$71.9341	$71.93	$71.95	$71.90
7 purchase totals =	$801.46		$870.9160	$870.91	$870.90	$870.80