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	$51.94	12.868%	$58.6236	$58.62	$58.60	$58.60
Purchase #2	$76.25	8.164%	$82.4751	$82.48	$82.50	$82.50
Purchase #3	$250.54	13.567%	$284.5308	$284.53	$284.55	$284.50
Purchase #4	$163.55	13.534%	$185.6849	$185.68	$185.70	$185.70
Purchase #5	$244.81	12.137%	$274.5226	$274.52	$274.50	$274.50
Purchase #6	$183.95	10.650%	$203.5407	$203.54	$203.55	$203.50
Purchase #7	$176.29	5.568%	$186.1058	$186.11	$186.10	$186.10
7 purchase totals =	$1,147.33		$1,275.4835	$1,275.48	$1,275.50	$1,275.40