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	$87.53	3.213%	$90.3423	$90.34	$90.35	$90.30
Purchase #2	$40.54	10.633%	$44.8506	$44.85	$44.85	$44.90
Purchase #3	$23.70	9.353%	$25.9167	$25.92	$25.90	$25.90
Purchase #4	$167.48	9.217%	$182.9166	$182.92	$182.90	$182.90
Purchase #5	$37.72	7.640%	$40.6018	$40.60	$40.60	$40.60
Purchase #6	$140.34	6.530%	$149.5042	$149.50	$149.50	$149.50
Purchase #7	$75.34	12.833%	$85.0084	$85.01	$85.00	$85.00
7 purchase totals =	$572.65		$619.1406	$619.14	$619.10	$619.10