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	$36.85	12.432%	$41.4312	$41.43	$41.45	$41.40
Purchase #2	$98.51	13.236%	$111.5488	$111.55	$111.55	$111.50
Purchase #3	$220.49	5.184%	$231.9202	$231.92	$231.90	$231.90
Purchase #4	$38.42	3.614%	$39.8085	$39.81	$39.80	$39.80
Purchase #5	$130.26	12.716%	$146.8239	$146.82	$146.80	$146.80
Purchase #6	$17.73	3.752%	$18.3952	$18.40	$18.40	$18.40
Purchase #7	$26.96	4.158%	$28.081	$28.08	$28.10	$28.10
7 purchase totals =	$569.22		$618.0088	$618.01	$618.00	$617.90