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	$68.89	13.811%	$78.4044	$78.40	$78.40	$78.40
Purchase #2	$36.51	11.717%	$40.7879	$40.79	$40.80	$40.80
Purchase #3	$40.59	11.298%	$45.1759	$45.18	$45.20	$45.20
Purchase #4	$33.75	9.326%	$36.8975	$36.90	$36.90	$36.90
Purchase #5	$184.68	3.601%	$191.3303	$191.33	$191.35	$191.30
Purchase #6	$78.90	5.585%	$83.3066	$83.31	$83.30	$83.30
Purchase #7	$125.65	4.282%	$131.0303	$131.03	$131.05	$131.00
7 purchase totals =	$568.97		$606.9329	$606.94	$607.00	$606.90