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	$237.67	12.726%	$267.9159	$267.92	$267.90	$267.90
Purchase #2	$59.81	8.414%	$64.8424	$64.84	$64.85	$64.80
Purchase #3	$13.90	10.450%	$15.3526	$15.35	$15.35	$15.40
Purchase #4	$85.70	5.638%	$90.5318	$90.53	$90.55	$90.50
Purchase #5	$150.43	9.843%	$165.2368	$165.24	$165.25	$165.20
Purchase #6	$86.37	8.762%	$93.9377	$93.94	$93.95	$93.90
Purchase #7	$157.78	9.417%	$172.6381	$172.64	$172.65	$172.60
7 purchase totals =	$791.66		$870.4553	$870.46	$870.50	$870.30