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	$36.28	12.201%	$40.7065	$40.71	$40.70	$40.70
Purchase #2	$76.28	10.196%	$84.0575	$84.06	$84.05	$84.10
Purchase #3	$83.37	13.366%	$94.5132	$94.51	$94.50	$94.50
Purchase #4	$48.40	11.652%	$54.0396	$54.04	$54.05	$54.00
Purchase #5	$54.72	8.650%	$59.4533	$59.45	$59.45	$59.50
Purchase #6	$249.89	4.461%	$261.0376	$261.04	$261.05	$261.00
Purchase #7	$249.93	11.700%	$279.1718	$279.17	$279.15	$279.20
7 purchase totals =	$798.87		$872.9795	$872.98	$872.95	$873.00