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	$80.25	13.351%	$90.9642	$90.96	$90.95	$91.00
Purchase #2	$156.66	8.867%	$170.551	$170.55	$170.55	$170.60
Purchase #3	$246.97	6.697%	$263.5096	$263.51	$263.50	$263.50
Purchase #4	$87.74	7.802%	$94.5855	$94.59	$94.60	$94.60
Purchase #5	$75.28	4.796%	$78.8904	$78.89	$78.90	$78.90
Purchase #6	$131.61	6.294%	$139.8935	$139.89	$139.90	$139.90
Purchase #7	$55.71	7.457%	$59.8643	$59.86	$59.85	$59.90
7 purchase totals =	$834.22		$898.2585	$898.25	$898.25	$898.40