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	$224.66	12.565%	$252.8885	$252.89	$252.90	$252.90
Purchase #2	$219.45	10.828%	$243.212	$243.21	$243.20	$243.20
Purchase #3	$153.79	5.540%	$162.31	$162.31	$162.30	$162.30
Purchase #4	$75.90	8.669%	$82.4798	$82.48	$82.50	$82.50
Purchase #5	$31.78	9.364%	$34.7559	$34.76	$34.75	$34.80
Purchase #6	$94.69	12.252%	$106.2914	$106.29	$106.30	$106.30
Purchase #7	$33.84	10.725%	$37.4693	$37.47	$37.45	$37.50
7 purchase totals =	$834.11		$919.4069	$919.41	$919.40	$919.50