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	$45.78	12.605%	$51.5506	$51.55	$51.55	$51.60
Purchase #2	$39.46	8.167%	$42.6827	$42.68	$42.70	$42.70
Purchase #3	$55.69	11.722%	$62.218	$62.22	$62.20	$62.20
Purchase #4	$141.81	9.676%	$155.5315	$155.53	$155.55	$155.50
Purchase #5	$35.59	8.213%	$38.513	$38.51	$38.50	$38.50
Purchase #6	$64.34	3.492%	$66.5868	$66.59	$66.60	$66.60
Purchase #7	$99.34	9.133%	$108.4127	$108.41	$108.40	$108.40
7 purchase totals =	$482.01		$525.4953	$525.49	$525.50	$525.50