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	$244.80	11.816%	$273.7256	$273.73	$273.75	$273.70
Purchase #2	$65.73	7.651%	$70.759	$70.76	$70.75	$70.80
Purchase #3	$127.95	7.563%	$137.6269	$137.63	$137.65	$137.60
Purchase #4	$73.42	10.831%	$81.3721	$81.37	$81.35	$81.40
Purchase #5	$81.74	9.439%	$89.4554	$89.46	$89.45	$89.50
Purchase #6	$66.94	8.582%	$72.6848	$72.68	$72.70	$72.70
Purchase #7	$205.28	7.768%	$221.2262	$221.23	$221.25	$221.20
7 purchase totals =	$865.86		$946.8500	$946.86	$946.90	$946.90