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	$186.40	5.594%	$196.8272	$196.83	$196.85	$196.80
Purchase #2	$83.96	7.804%	$90.5122	$90.51	$90.50	$90.50
Purchase #3	$113.66	12.217%	$127.5458	$127.55	$127.55	$127.50
Purchase #4	$98.71	8.861%	$107.4567	$107.46	$107.45	$107.50
Purchase #5	$230.77	7.574%	$248.2485	$248.25	$248.25	$248.20
Purchase #6	$136.57	11.263%	$151.9519	$151.95	$151.95	$152.00
Purchase #7	$52.38	9.777%	$57.5012	$57.50	$57.50	$57.50
7 purchase totals =	$902.45		$980.0435	$980.05	$980.05	$980.00