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	$87.84	13.284%	$99.5087	$99.51	$99.50	$99.50
Purchase #2	$56.63	7.712%	$60.9973	$61.00	$61.00	$61.00
Purchase #3	$201.77	9.178%	$220.2885	$220.29	$220.30	$220.30
Purchase #4	$175.96	8.390%	$190.723	$190.72	$190.70	$190.70
Purchase #5	$88.72	11.693%	$99.094	$99.09	$99.10	$99.10
Purchase #6	$154.99	10.669%	$171.5259	$171.53	$171.55	$171.50
Purchase #7	$22.91	12.417%	$25.7547	$25.75	$25.75	$25.80
7 purchase totals =	$788.82		$867.8921	$867.89	$867.90	$867.90