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	$209.85	7.154%	$224.8627	$224.86	$224.85	$224.90
Purchase #2	$18.43	8.293%	$19.9584	$19.96	$19.95	$20.00
Purchase #3	$103.85	12.628%	$116.9642	$116.96	$116.95	$117.00
Purchase #4	$85.53	6.192%	$90.826	$90.83	$90.85	$90.80
Purchase #5	$102.30	9.162%	$111.6727	$111.67	$111.65	$111.70
Purchase #6	$33.36	6.871%	$35.6522	$35.65	$35.65	$35.70
Purchase #7	$236.35	10.807%	$261.8923	$261.89	$261.90	$261.90
7 purchase totals =	$789.67		$861.8285	$861.82	$861.80	$862.00