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	$222.66	6.389%	$236.8857	$236.89	$236.90	$236.90
Purchase #2	$117.43	12.809%	$132.4716	$132.47	$132.45	$132.50
Purchase #3	$243.61	8.513%	$264.3485	$264.35	$264.35	$264.30
Purchase #4	$148.69	8.646%	$161.5457	$161.55	$161.55	$161.50
Purchase #5	$29.92	6.217%	$31.7801	$31.78	$31.80	$31.80
Purchase #6	$209.47	11.644%	$233.8607	$233.86	$233.85	$233.90
Purchase #7	$146.75	5.611%	$154.9841	$154.98	$155.00	$155.00
7 purchase totals =	$1,118.53		$1,215.8764	$1,215.88	$1,215.90	$1,215.90