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	$41.82	3.247%	$43.1779	$43.18	$43.20	$43.20
Purchase #2	$175.30	9.218%	$191.4592	$191.46	$191.45	$191.50
Purchase #3	$188.73	13.866%	$214.8993	$214.90	$214.90	$214.90
Purchase #4	$188.51	8.603%	$204.7275	$204.73	$204.75	$204.70
Purchase #5	$169.96	13.607%	$193.0865	$193.09	$193.10	$193.10
Purchase #6	$157.55	7.785%	$169.8153	$169.82	$169.80	$169.80
Purchase #7	$78.88	5.618%	$83.3115	$83.31	$83.30	$83.30
7 purchase totals =	$1,000.75		$1,100.4772	$1,100.49	$1,100.50	$1,100.50