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	$47.29	7.677%	$50.9205	$50.92	$50.90	$50.90
Purchase #2	$20.79	3.587%	$21.5357	$21.54	$21.55	$21.50
Purchase #3	$153.49	11.738%	$171.5067	$171.51	$171.50	$171.50
Purchase #4	$167.43	5.209%	$176.1514	$176.15	$176.15	$176.20
Purchase #5	$155.66	13.215%	$176.2305	$176.23	$176.25	$176.20
Purchase #6	$160.25	7.271%	$171.9018	$171.90	$171.90	$171.90
Purchase #7	$108.76	4.271%	$113.4051	$113.41	$113.40	$113.40
7 purchase totals =	$813.67		$881.6517	$881.66	$881.65	$881.60