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	$28.93	12.443%	$32.5298	$32.53	$32.55	$32.50
Purchase #2	$131.36	10.669%	$145.3748	$145.37	$145.35	$145.40
Purchase #3	$42.95	11.589%	$47.9275	$47.93	$47.95	$47.90
Purchase #4	$116.93	5.624%	$123.5061	$123.51	$123.50	$123.50
Purchase #5	$158.73	7.556%	$170.7236	$170.72	$170.70	$170.70
Purchase #6	$12.27	5.552%	$12.9512	$12.95	$12.95	$13.00
Purchase #7	$163.36	3.150%	$168.5058	$168.51	$168.50	$168.50
7 purchase totals =	$654.53		$701.5188	$701.52	$701.50	$701.50