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	$8.90	9.731%	$9.7661	$9.77	$9.75	$9.80
Purchase #2	$218.78	10.797%	$242.4017	$242.40	$242.40	$242.40
Purchase #3	$140.45	4.248%	$146.4163	$146.42	$146.40	$146.40
Purchase #4	$129.31	7.473%	$138.9733	$138.97	$138.95	$139.00
Purchase #5	$247.52	12.403%	$278.2199	$278.22	$278.20	$278.20
Purchase #6	$126.96	9.846%	$139.4605	$139.46	$139.45	$139.50
Purchase #7	$130.35	11.141%	$144.8723	$144.87	$144.85	$144.90
7 purchase totals =	$1,002.27		$1,100.1101	$1,100.11	$1,100.00	$1,100.20