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	$88.91	13.256%	$100.6959	$100.70	$100.70	$100.70
Purchase #2	$223.52	13.268%	$253.1766	$253.18	$253.20	$253.20
Purchase #3	$131.89	13.531%	$149.736	$149.74	$149.75	$149.70
Purchase #4	$236.57	7.126%	$253.428	$253.43	$253.45	$253.40
Purchase #5	$72.76	12.166%	$81.612	$81.61	$81.60	$81.60
Purchase #6	$208.95	7.148%	$223.8857	$223.89	$223.90	$223.90
Purchase #7	$34.59	9.131%	$37.7484	$37.75	$37.75	$37.70
7 purchase totals =	$997.19		$1,100.2826	$1,100.30	$1,100.35	$1,100.20