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	$246.25	13.254%	$278.888	$278.89	$278.90	$278.90
Purchase #2	$250.81	8.372%	$271.8078	$271.81	$271.80	$271.80
Purchase #3	$71.48	11.229%	$79.5065	$79.51	$79.50	$79.50
Purchase #4	$242.69	5.590%	$256.2564	$256.26	$256.25	$256.30
Purchase #5	$150.60	9.266%	$164.5546	$164.55	$164.55	$164.60
Purchase #6	$96.64	13.714%	$109.8932	$109.89	$109.90	$109.90
Purchase #7	$199.64	11.248%	$222.0955	$222.10	$222.10	$222.10
7 purchase totals =	$1,258.11		$1,383.0020	$1,383.01	$1,383.00	$1,383.10