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	$19.25	9.605%	$21.099	$21.10	$21.10	$21.10
Purchase #2	$66.68	7.453%	$71.6497	$71.65	$71.65	$71.60
Purchase #3	$171.69	9.795%	$188.507	$188.51	$188.50	$188.50
Purchase #4	$87.54	11.331%	$97.4592	$97.46	$97.45	$97.50
Purchase #5	$121.77	8.518%	$132.1424	$132.14	$132.15	$132.10
Purchase #6	$91.59	8.498%	$99.3733	$99.37	$99.35	$99.40
Purchase #7	$186.99	5.198%	$196.7097	$196.71	$196.70	$196.70
7 purchase totals =	$745.51		$806.9403	$806.94	$806.90	$806.90