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	$131.34	4.652%	$137.4499	$137.45	$137.45	$137.40
Purchase #2	$37.37	13.477%	$42.4064	$42.41	$42.40	$42.40
Purchase #3	$101.67	7.539%	$109.3349	$109.33	$109.35	$109.30
Purchase #4	$133.67	8.156%	$144.5721	$144.57	$144.55	$144.60
Purchase #5	$213.80	11.615%	$238.6329	$238.63	$238.65	$238.60
Purchase #6	$65.96	10.339%	$72.7796	$72.78	$72.80	$72.80
Purchase #7	$213.25	12.654%	$240.2347	$240.23	$240.25	$240.20
7 purchase totals =	$897.06		$985.4105	$985.40	$985.45	$985.30