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	$18.47	11.699%	$20.6308	$20.63	$20.65	$20.60
Purchase #2	$161.34	10.872%	$178.8809	$178.88	$178.90	$178.90
Purchase #3	$71.70	13.750%	$81.5588	$81.56	$81.55	$81.60
Purchase #4	$143.35	13.594%	$162.837	$162.84	$162.85	$162.80
Purchase #5	$32.87	3.468%	$34.0099	$34.01	$34.00	$34.00
Purchase #6	$17.82	11.726%	$19.9096	$19.91	$19.90	$19.90
Purchase #7	$67.34	8.256%	$72.8996	$72.90	$72.90	$72.90
7 purchase totals =	$512.89		$570.7266	$570.73	$570.75	$570.70