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	$120.61	12.105%	$135.2098	$135.21	$135.20	$135.20
Purchase #2	$125.40	11.799%	$140.1959	$140.20	$140.20	$140.20
Purchase #3	$52.69	12.539%	$59.2968	$59.30	$59.30	$59.30
Purchase #4	$111.47	8.496%	$120.9405	$120.94	$120.95	$120.90
Purchase #5	$181.39	3.113%	$187.0367	$187.04	$187.05	$187.00
Purchase #6	$137.38	10.341%	$151.5865	$151.59	$151.60	$151.60
Purchase #7	$206.66	5.756%	$218.5553	$218.56	$218.55	$218.60
7 purchase totals =	$935.60		$1,012.8215	$1,012.84	$1,012.85	$1,012.80