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	$227.84	12.726%	$256.8349	$256.83	$256.85	$256.80
Purchase #2	$38.56	10.584%	$42.6412	$42.64	$42.65	$42.60
Purchase #3	$116.63	12.518%	$131.2297	$131.23	$131.25	$131.20
Purchase #4	$151.70	12.340%	$170.4198	$170.42	$170.40	$170.40
Purchase #5	$219.50	8.374%	$237.8809	$237.88	$237.90	$237.90
Purchase #6	$227.58	7.664%	$245.0217	$245.02	$245.00	$245.00
Purchase #7	$38.59	11.185%	$42.9063	$42.91	$42.90	$42.90
7 purchase totals =	$1,020.40		$1,126.9345	$1,126.93	$1,126.95	$1,126.80