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	$38.39	11.588%	$42.8386	$42.84	$42.85	$42.80
Purchase #2	$75.77	3.419%	$78.3606	$78.36	$78.35	$78.40
Purchase #3	$113.68	8.280%	$123.0927	$123.09	$123.10	$123.10
Purchase #4	$103.59	12.369%	$116.403	$116.40	$116.40	$116.40
Purchase #5	$5.67	11.468%	$6.3202	$6.32	$6.30	$6.30
Purchase #6	$90.68	3.871%	$94.1902	$94.19	$94.20	$94.20
Purchase #7	$60.83	8.540%	$66.0249	$66.02	$66.00	$66.00
7 purchase totals =	$488.61		$527.2302	$527.22	$527.20	$527.20