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	$193.39	13.158%	$218.8363	$218.84	$218.85	$218.80
Purchase #2	$244.55	12.590%	$275.3388	$275.34	$275.35	$275.30
Purchase #3	$70.76	13.770%	$80.5037	$80.50	$80.50	$80.50
Purchase #4	$224.46	8.709%	$244.0082	$244.01	$244.00	$244.00
Purchase #5	$157.43	9.205%	$171.9214	$171.92	$171.90	$171.90
Purchase #6	$42.57	13.387%	$48.2688	$48.27	$48.25	$48.30
Purchase #7	$131.78	7.275%	$141.367	$141.37	$141.35	$141.40
7 purchase totals =	$1,064.94		$1,180.2442	$1,180.25	$1,180.20	$1,180.20