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	$240.94	6.201%	$255.8807	$255.88	$255.90	$255.90
Purchase #2	$38.30	11.480%	$42.6968	$42.70	$42.70	$42.70
Purchase #3	$184.58	7.407%	$198.2518	$198.25	$198.25	$198.30
Purchase #4	$232.37	13.168%	$262.9685	$262.97	$262.95	$263.00
Purchase #5	$47.78	7.714%	$51.4657	$51.47	$51.45	$51.50
Purchase #6	$124.96	7.484%	$134.312	$134.31	$134.30	$134.30
Purchase #7	$159.73	5.513%	$168.5359	$168.54	$168.55	$168.50
7 purchase totals =	$1,028.66		$1,114.1114	$1,114.12	$1,114.10	$1,114.20