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	$234.27	10.308%	$258.4186	$258.42	$258.40	$258.40
Purchase #2	$172.53	9.569%	$189.0394	$189.04	$189.05	$189.00
Purchase #3	$81.94	10.427%	$90.4839	$90.48	$90.50	$90.50
Purchase #4	$39.64	11.841%	$44.3338	$44.33	$44.35	$44.30
Purchase #5	$139.41	10.326%	$153.8055	$153.81	$153.80	$153.80
Purchase #6	$59.90	5.619%	$63.2658	$63.27	$63.25	$63.30
Purchase #7	$10.63	7.203%	$11.3957	$11.40	$11.40	$11.40
7 purchase totals =	$738.32		$810.7427	$810.75	$810.75	$810.70