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	$128.30	6.477%	$136.61	$136.61	$136.60	$136.60
Purchase #2	$129.51	9.595%	$141.9365	$141.94	$141.95	$141.90
Purchase #3	$77.82	9.385%	$85.1234	$85.12	$85.10	$85.10
Purchase #4	$40.58	12.811%	$45.7787	$45.78	$45.80	$45.80
Purchase #5	$54.51	5.134%	$57.3085	$57.31	$57.30	$57.30
Purchase #6	$23.99	7.778%	$25.8559	$25.86	$25.85	$25.90
Purchase #7	$108.27	9.267%	$118.3034	$118.30	$118.30	$118.30
7 purchase totals =	$562.98		$610.9164	$610.92	$610.90	$610.90