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	$38.38	4.807%	$40.2249	$40.22	$40.20	$40.20
Purchase #2	$26.88	7.367%	$28.8602	$28.86	$28.85	$28.90
Purchase #3	$50.88	7.102%	$54.4935	$54.49	$54.50	$54.50
Purchase #4	$110.53	11.707%	$123.4697	$123.47	$123.45	$123.50
Purchase #5	$195.45	3.282%	$201.8647	$201.86	$201.85	$201.90
Purchase #6	$6.89	3.444%	$7.1273	$7.13	$7.15	$7.10
Purchase #7	$75.61	9.751%	$82.9827	$82.98	$83.00	$83.00
7 purchase totals =	$504.62		$539.0230	$539.01	$539.00	$539.10