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	$210.53	9.808%	$231.1788	$231.18	$231.20	$231.20
Purchase #2	$95.77	4.870%	$100.434	$100.43	$100.45	$100.40
Purchase #3	$36.82	10.748%	$40.7774	$40.78	$40.80	$40.80
Purchase #4	$188.34	11.270%	$209.5659	$209.57	$209.55	$209.60
Purchase #5	$102.25	5.568%	$107.9433	$107.94	$107.95	$107.90
Purchase #6	$9.56	12.157%	$10.7222	$10.72	$10.70	$10.70
Purchase #7	$38.76	10.575%	$42.8589	$42.86	$42.85	$42.90
7 purchase totals =	$682.03		$743.4805	$743.48	$743.50	$743.50