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	$7.57	3.838%	$7.8605	$7.86	$7.85	$7.90
Purchase #2	$64.48	3.198%	$66.5421	$66.54	$66.55	$66.50
Purchase #3	$250.77	4.809%	$262.8295	$262.83	$262.85	$262.80
Purchase #4	$110.80	7.199%	$118.7765	$118.78	$118.80	$118.80
Purchase #5	$55.89	5.833%	$59.1501	$59.15	$59.15	$59.20
Purchase #6	$140.96	9.330%	$154.1116	$154.11	$154.10	$154.10
Purchase #7	$212.50	9.584%	$232.866	$232.87	$232.85	$232.90
7 purchase totals =	$842.97		$902.1363	$902.14	$902.15	$902.20