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	$29.51	6.385%	$31.3942	$31.39	$31.40	$31.40
Purchase #2	$139.82	12.786%	$157.6974	$157.70	$157.70	$157.70
Purchase #3	$19.49	7.143%	$20.8822	$20.88	$20.90	$20.90
Purchase #4	$54.50	9.762%	$59.8203	$59.82	$59.80	$59.80
Purchase #5	$91.65	7.159%	$98.2112	$98.21	$98.20	$98.20
Purchase #6	$223.89	3.139%	$230.9179	$230.92	$230.90	$230.90
Purchase #7	$240.90	8.682%	$261.8149	$261.81	$261.80	$261.80
7 purchase totals =	$799.76		$860.7381	$860.73	$860.70	$860.70