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	$85.85	4.311%	$89.551	$89.55	$89.55	$89.60
Purchase #2	$121.45	12.362%	$136.4636	$136.46	$136.45	$136.50
Purchase #3	$34.59	7.569%	$37.2081	$37.21	$37.20	$37.20
Purchase #4	$171.40	3.767%	$177.8566	$177.86	$177.85	$177.90
Purchase #5	$171.26	13.766%	$194.8357	$194.84	$194.85	$194.80
Purchase #6	$10.64	12.300%	$11.9487	$11.95	$11.95	$11.90
Purchase #7	$184.59	8.770%	$200.7785	$200.78	$200.80	$200.80
7 purchase totals =	$779.78		$848.6422	$848.65	$848.65	$848.70