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	$104.38	6.602%	$111.2712	$111.27	$111.25	$111.30
Purchase #2	$152.59	12.470%	$171.618	$171.62	$171.60	$171.60
Purchase #3	$57.37	10.630%	$63.4684	$63.47	$63.45	$63.50
Purchase #4	$145.39	4.403%	$151.7915	$151.79	$151.80	$151.80
Purchase #5	$84.41	10.429%	$93.2131	$93.21	$93.20	$93.20
Purchase #6	$63.38	8.249%	$68.6082	$68.61	$68.60	$68.60
Purchase #7	$6.89	3.546%	$7.1343	$7.13	$7.15	$7.10
7 purchase totals =	$614.41		$667.1047	$667.10	$667.05	$667.10