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	$40.51	5.492%	$42.7348	$42.73	$42.75	$42.70
Purchase #2	$93.32	13.351%	$105.7792	$105.78	$105.80	$105.80
Purchase #3	$40.49	12.138%	$45.4047	$45.40	$45.40	$45.40
Purchase #4	$178.40	11.844%	$199.5297	$199.53	$199.55	$199.50
Purchase #5	$97.67	13.351%	$110.7099	$110.71	$110.70	$110.70
Purchase #6	$227.76	5.437%	$240.1433	$240.14	$240.15	$240.10
Purchase #7	$193.45	3.758%	$200.7199	$200.72	$200.70	$200.70
7 purchase totals =	$871.60		$945.0215	$945.01	$945.05	$944.90