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	$233.78	3.599%	$242.1937	$242.19	$242.20	$242.20
Purchase #2	$52.85	11.707%	$59.0371	$59.04	$59.05	$59.00
Purchase #3	$202.70	9.752%	$222.4673	$222.47	$222.45	$222.50
Purchase #4	$140.62	13.536%	$159.6543	$159.65	$159.65	$159.70
Purchase #5	$83.72	3.358%	$86.5313	$86.53	$86.55	$86.50
Purchase #6	$103.50	6.848%	$110.5877	$110.59	$110.60	$110.60
Purchase #7	$13.73	12.434%	$15.4372	$15.44	$15.45	$15.40
7 purchase totals =	$830.90		$895.9086	$895.91	$895.95	$895.90