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	$140.90	6.867%	$150.5756	$150.58	$150.60	$150.60
Purchase #2	$153.43	10.175%	$169.0415	$169.04	$169.05	$169.00
Purchase #3	$129.79	7.332%	$139.3062	$139.31	$139.30	$139.30
Purchase #4	$131.53	11.309%	$146.4047	$146.40	$146.40	$146.40
Purchase #5	$30.76	4.345%	$32.0965	$32.10	$32.10	$32.10
Purchase #6	$45.34	7.843%	$48.896	$48.90	$48.90	$48.90
Purchase #7	$7.85	3.846%	$8.1519	$8.15	$8.15	$8.20
7 purchase totals =	$639.60		$694.4724	$694.48	$694.50	$694.50