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	$69.87	11.851%	$78.1503	$78.15	$78.15	$78.20
Purchase #2	$94.94	10.811%	$105.204	$105.20	$105.20	$105.20
Purchase #3	$115.54	5.311%	$121.6763	$121.68	$121.70	$121.70
Purchase #4	$187.63	13.761%	$213.4498	$213.45	$213.45	$213.40
Purchase #5	$51.44	11.801%	$57.5104	$57.51	$57.50	$57.50
Purchase #6	$64.41	3.593%	$66.7243	$66.72	$66.70	$66.70
Purchase #7	$176.78	11.165%	$196.5175	$196.52	$196.50	$196.50
7 purchase totals =	$760.61		$839.2326	$839.23	$839.20	$839.20