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	$186.26	6.861%	$199.0393	$199.04	$199.05	$199.00
Purchase #2	$136.37	6.526%	$145.2695	$145.27	$145.25	$145.30
Purchase #3	$107.28	10.519%	$118.5648	$118.56	$118.55	$118.60
Purchase #4	$71.55	9.384%	$78.2643	$78.26	$78.25	$78.30
Purchase #5	$28.77	10.553%	$31.8061	$31.81	$31.80	$31.80
Purchase #6	$126.89	13.251%	$143.7042	$143.70	$143.70	$143.70
Purchase #7	$156.70	7.342%	$168.2049	$168.20	$168.20	$168.20
7 purchase totals =	$813.82		$884.8531	$884.84	$884.80	$884.90