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	$29.37	11.540%	$32.7593	$32.76	$32.75	$32.80
Purchase #2	$83.61	4.138%	$87.0698	$87.07	$87.05	$87.10
Purchase #3	$34.66	9.463%	$37.9399	$37.94	$37.95	$37.90
Purchase #4	$23.71	3.435%	$24.5244	$24.52	$24.50	$24.50
Purchase #5	$63.85	9.427%	$69.8691	$69.87	$69.85	$69.90
Purchase #6	$14.50	9.595%	$15.8913	$15.89	$15.90	$15.90
Purchase #7	$6.84	8.465%	$7.419	$7.42	$7.40	$7.40
7 purchase totals =	$256.54		$275.4728	$275.47	$275.40	$275.50