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	$91.83	7.411%	$98.6355	$98.64	$98.65	$98.60
Purchase #2	$124.50	6.410%	$132.4805	$132.48	$132.50	$132.50
Purchase #3	$177.82	12.788%	$200.5596	$200.56	$200.55	$200.60
Purchase #4	$243.33	12.814%	$274.5103	$274.51	$274.50	$274.50
Purchase #5	$47.67	10.729%	$52.7845	$52.78	$52.80	$52.80
Purchase #6	$90.45	11.655%	$100.9919	$100.99	$101.00	$101.00
Purchase #7	$72.32	3.628%	$74.9438	$74.94	$74.95	$74.90
7 purchase totals =	$847.92		$934.9061	$934.90	$934.95	$934.90