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	$116.85	12.312%	$131.2366	$131.24	$131.25	$131.20
Purchase #2	$36.94	11.263%	$41.1006	$41.10	$41.10	$41.10
Purchase #3	$212.60	10.680%	$235.3057	$235.31	$235.30	$235.30
Purchase #4	$111.57	6.807%	$119.1646	$119.16	$119.15	$119.20
Purchase #5	$63.86	4.734%	$66.8831	$66.88	$66.90	$66.90
Purchase #6	$188.66	5.704%	$199.4212	$199.42	$199.40	$199.40
Purchase #7	$53.89	3.728%	$55.899	$55.90	$55.90	$55.90
7 purchase totals =	$784.37		$849.0108	$849.01	$849.00	$849.00