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	$250.63	12.349%	$281.5803	$281.58	$281.60	$281.60
Purchase #2	$67.94	9.639%	$74.4887	$74.49	$74.50	$74.50
Purchase #3	$166.38	7.271%	$178.4775	$178.48	$178.50	$178.50
Purchase #4	$44.74	6.331%	$47.5725	$47.57	$47.55	$47.60
Purchase #5	$94.83	6.439%	$100.9361	$100.94	$100.95	$100.90
Purchase #6	$156.81	5.530%	$165.4816	$165.48	$165.50	$165.50
Purchase #7	$199.34	9.175%	$217.6294	$217.63	$217.65	$217.60
7 purchase totals =	$980.67		$1,066.1661	$1,066.17	$1,066.25	$1,066.20