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	$184.28	6.441%	$196.1495	$196.15	$196.15	$196.10
Purchase #2	$30.79	11.556%	$34.3481	$34.35	$34.35	$34.30
Purchase #3	$208.25	9.226%	$227.4631	$227.46	$227.45	$227.50
Purchase #4	$242.96	13.282%	$275.2299	$275.23	$275.25	$275.20
Purchase #5	$132.54	10.345%	$146.2513	$146.25	$146.25	$146.30
Purchase #6	$99.99	12.183%	$112.1718	$112.17	$112.15	$112.20
Purchase #7	$5.68	11.746%	$6.3472	$6.35	$6.35	$6.30
7 purchase totals =	$904.49		$997.9609	$997.96	$997.95	$997.90