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	$29.90	12.792%	$33.7248	$33.72	$33.70	$33.70
Purchase #2	$144.75	13.317%	$164.0264	$164.03	$164.05	$164.00
Purchase #3	$18.66	9.715%	$20.4728	$20.47	$20.45	$20.50
Purchase #4	$191.40	3.727%	$198.5335	$198.53	$198.55	$198.50
Purchase #5	$95.79	3.684%	$99.3189	$99.32	$99.30	$99.30
Purchase #6	$138.42	4.821%	$145.0932	$145.09	$145.10	$145.10
Purchase #7	$236.67	10.648%	$261.8706	$261.87	$261.85	$261.90
7 purchase totals =	$855.59		$923.0402	$923.03	$923.00	$923.00