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	$144.61	4.290%	$150.8138	$150.81	$150.80	$150.80
Purchase #2	$49.84	9.769%	$54.7089	$54.71	$54.70	$54.70
Purchase #3	$176.45	12.794%	$199.025	$199.03	$199.05	$199.00
Purchase #4	$202.98	9.677%	$222.6224	$222.62	$222.60	$222.60
Purchase #5	$96.93	8.807%	$105.4666	$105.47	$105.45	$105.50
Purchase #6	$75.73	11.582%	$84.501	$84.50	$84.50	$84.50
Purchase #7	$103.61	10.783%	$114.7823	$114.78	$114.80	$114.80
7 purchase totals =	$850.15		$931.9200	$931.92	$931.90	$931.90