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	$29.40	11.734%	$32.8498	$32.85	$32.85	$32.80
Purchase #2	$201.44	4.500%	$210.5048	$210.50	$210.50	$210.50
Purchase #3	$213.55	13.401%	$242.1678	$242.17	$242.15	$242.20
Purchase #4	$43.40	4.820%	$45.4919	$45.49	$45.50	$45.50
Purchase #5	$131.65	13.497%	$149.4188	$149.42	$149.40	$149.40
Purchase #6	$63.41	7.310%	$68.0453	$68.05	$68.05	$68.00
Purchase #7	$85.54	5.774%	$90.4791	$90.48	$90.50	$90.50
7 purchase totals =	$768.39		$838.9575	$838.96	$838.95	$838.90