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	$83.50	12.686%	$94.0928	$94.09	$94.10	$94.10
Purchase #2	$81.43	10.467%	$89.9533	$89.95	$89.95	$90.00
Purchase #3	$234.41	3.621%	$242.898	$242.90	$242.90	$242.90
Purchase #4	$125.90	4.637%	$131.738	$131.74	$131.75	$131.70
Purchase #5	$92.51	6.630%	$98.6434	$98.64	$98.65	$98.60
Purchase #6	$199.80	8.858%	$217.4983	$217.50	$217.50	$217.50
Purchase #7	$54.25	8.867%	$59.0603	$59.06	$59.05	$59.10
7 purchase totals =	$871.80		$933.8841	$933.88	$933.90	$933.90