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	$112.73	3.607%	$116.7962	$116.80	$116.80	$116.80
Purchase #2	$36.43	12.241%	$40.8894	$40.89	$40.90	$40.90
Purchase #3	$40.66	12.321%	$45.6697	$45.67	$45.65	$45.70
Purchase #4	$126.57	13.312%	$143.419	$143.42	$143.40	$143.40
Purchase #5	$13.76	8.227%	$14.892	$14.89	$14.90	$14.90
Purchase #6	$64.65	8.502%	$70.1465	$70.15	$70.15	$70.10
Purchase #7	$214.94	5.376%	$226.4952	$226.50	$226.50	$226.50
7 purchase totals =	$609.74		$658.3080	$658.32	$658.30	$658.30