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	$60.54	11.768%	$67.6643	$67.66	$67.65	$67.70
Purchase #2	$226.30	6.264%	$240.4754	$240.48	$240.50	$240.50
Purchase #3	$204.35	4.452%	$213.4477	$213.45	$213.45	$213.40
Purchase #4	$219.94	8.219%	$238.0169	$238.02	$238.00	$238.00
Purchase #5	$220.72	13.839%	$251.2654	$251.27	$251.25	$251.30
Purchase #6	$242.51	13.437%	$275.0961	$275.10	$275.10	$275.10
Purchase #7	$106.54	6.526%	$113.4928	$113.49	$113.50	$113.50
7 purchase totals =	$1,280.90		$1,399.4586	$1,399.47	$1,399.45	$1,399.50