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	$31.89	9.211%	$34.8274	$34.83	$34.85	$34.80
Purchase #2	$144.51	4.788%	$151.4291	$151.43	$151.45	$151.40
Purchase #3	$25.56	9.759%	$28.0544	$28.05	$28.05	$28.10
Purchase #4	$27.84	12.111%	$31.2117	$31.21	$31.20	$31.20
Purchase #5	$52.65	5.317%	$55.4494	$55.45	$55.45	$55.40
Purchase #6	$59.95	11.270%	$66.7064	$66.71	$66.70	$66.70
Purchase #7	$25.72	8.393%	$27.8787	$27.88	$27.90	$27.90
7 purchase totals =	$368.12		$395.5571	$395.56	$395.60	$395.50