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	$88.51	6.422%	$94.1941	$94.19	$94.20	$94.20
Purchase #2	$146.63	12.340%	$164.7241	$164.72	$164.70	$164.70
Purchase #3	$168.94	5.654%	$178.4919	$178.49	$178.50	$178.50
Purchase #4	$139.46	9.648%	$152.9151	$152.92	$152.90	$152.90
Purchase #5	$19.89	4.500%	$20.7851	$20.79	$20.80	$20.80
Purchase #6	$169.54	12.576%	$190.8614	$190.86	$190.85	$190.90
Purchase #7	$167.77	8.490%	$182.0137	$182.01	$182.00	$182.00
7 purchase totals =	$900.74		$983.9854	$983.98	$983.95	$984.00