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	$32.72	3.360%	$33.8194	$33.82	$33.80	$33.80
Purchase #2	$242.89	9.229%	$265.3063	$265.31	$265.30	$265.30
Purchase #3	$239.44	11.425%	$266.796	$266.80	$266.80	$266.80
Purchase #4	$141.44	6.400%	$150.4922	$150.49	$150.50	$150.50
Purchase #5	$161.37	4.630%	$168.8414	$168.84	$168.85	$168.80
Purchase #6	$117.43	12.840%	$132.508	$132.51	$132.50	$132.50
Purchase #7	$17.38	6.169%	$18.4522	$18.45	$18.45	$18.50
7 purchase totals =	$952.67		$1,036.2155	$1,036.22	$1,036.20	$1,036.20