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	$218.41	6.456%	$232.5105	$232.51	$232.50	$232.50
Purchase #2	$199.77	8.218%	$216.1871	$216.19	$216.20	$216.20
Purchase #3	$158.35	4.297%	$165.1543	$165.15	$165.15	$165.20
Purchase #4	$30.32	3.534%	$31.3915	$31.39	$31.40	$31.40
Purchase #5	$63.41	12.766%	$71.5049	$71.50	$71.50	$71.50
Purchase #6	$188.34	4.319%	$196.4744	$196.47	$196.45	$196.50
Purchase #7	$81.38	5.458%	$85.8217	$85.82	$85.80	$85.80
7 purchase totals =	$939.98		$999.0444	$999.03	$999.00	$999.10