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	$227.38	10.182%	$250.5318	$250.53	$250.55	$250.50
Purchase #2	$71.83	9.739%	$78.8255	$78.83	$78.85	$78.80
Purchase #3	$44.31	13.281%	$50.1948	$50.19	$50.20	$50.20
Purchase #4	$91.80	9.127%	$100.1786	$100.18	$100.20	$100.20
Purchase #5	$180.82	10.181%	$199.2293	$199.23	$199.25	$199.20
Purchase #6	$8.83	12.134%	$9.9014	$9.90	$9.90	$9.90
Purchase #7	$20.29	6.463%	$21.6013	$21.60	$21.60	$21.60
7 purchase totals =	$645.26		$710.4627	$710.46	$710.55	$710.40