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	$240.59	13.707%	$273.5677	$273.57	$273.55	$273.60
Purchase #2	$240.90	10.638%	$266.5269	$266.53	$266.55	$266.50
Purchase #3	$88.48	8.583%	$96.0742	$96.07	$96.05	$96.10
Purchase #4	$176.32	7.162%	$188.948	$188.95	$188.95	$188.90
Purchase #5	$124.40	10.766%	$137.7929	$137.79	$137.80	$137.80
Purchase #6	$72.74	13.612%	$82.6414	$82.64	$82.65	$82.60
Purchase #7	$157.26	5.660%	$166.1609	$166.16	$166.15	$166.20
7 purchase totals =	$1,100.69		$1,211.7120	$1,211.71	$1,211.70	$1,211.70