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	$89.45	12.860%	$100.9533	$100.95	$100.95	$101.00
Purchase #2	$179.89	11.291%	$200.2014	$200.20	$200.20	$200.20
Purchase #3	$23.47	10.615%	$25.9613	$25.96	$25.95	$26.00
Purchase #4	$106.95	4.611%	$111.8815	$111.88	$111.90	$111.90
Purchase #5	$87.62	8.310%	$94.9012	$94.90	$94.90	$94.90
Purchase #6	$65.58	10.482%	$72.4541	$72.45	$72.45	$72.50
Purchase #7	$55.44	7.625%	$59.6673	$59.67	$59.65	$59.70
7 purchase totals =	$608.40		$666.0201	$666.01	$666.00	$666.20