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	$11.82	9.583%	$12.9527	$12.95	$12.95	$13.00
Purchase #2	$177.30	13.853%	$201.8614	$201.86	$201.85	$201.90
Purchase #3	$92.69	6.259%	$98.4915	$98.49	$98.50	$98.50
Purchase #4	$250.78	9.570%	$274.7796	$274.78	$274.80	$274.80
Purchase #5	$244.84	7.318%	$262.7574	$262.76	$262.75	$262.80
Purchase #6	$20.96	3.374%	$21.6672	$21.67	$21.65	$21.70
Purchase #7	$123.45	6.317%	$131.2483	$131.25	$131.25	$131.20
7 purchase totals =	$921.84		$1,003.7581	$1,003.76	$1,003.75	$1,003.90