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	$59.83	4.337%	$62.4248	$62.42	$62.40	$62.40
Purchase #2	$37.87	7.492%	$40.7072	$40.71	$40.70	$40.70
Purchase #3	$210.79	3.455%	$218.0728	$218.07	$218.05	$218.10
Purchase #4	$123.38	12.842%	$139.2245	$139.22	$139.20	$139.20
Purchase #5	$126.44	10.207%	$139.3457	$139.35	$139.35	$139.30
Purchase #6	$35.75	5.427%	$37.6902	$37.69	$37.70	$37.70
Purchase #7	$77.81	4.576%	$81.3706	$81.37	$81.35	$81.40
7 purchase totals =	$671.87		$718.8358	$718.83	$718.75	$718.80