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	$128.27	10.624%	$141.8974	$141.90	$141.90	$141.90
Purchase #2	$160.53	10.118%	$176.7724	$176.77	$176.75	$176.80
Purchase #3	$107.94	6.488%	$114.9431	$114.94	$114.95	$114.90
Purchase #4	$94.30	9.620%	$103.3717	$103.37	$103.35	$103.40
Purchase #5	$41.36	3.622%	$42.8581	$42.86	$42.85	$42.90
Purchase #6	$221.90	13.777%	$252.4712	$252.47	$252.45	$252.50
Purchase #7	$38.96	10.639%	$43.105	$43.11	$43.10	$43.10
7 purchase totals =	$793.26		$875.4189	$875.42	$875.35	$875.50