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	$22.45	8.590%	$24.3785	$24.38	$24.40	$24.40
Purchase #2	$98.79	10.542%	$109.2044	$109.20	$109.20	$109.20
Purchase #3	$27.53	12.426%	$30.9509	$30.95	$30.95	$31.00
Purchase #4	$26.47	5.129%	$27.8276	$27.83	$27.85	$27.80
Purchase #5	$191.89	8.667%	$208.5211	$208.52	$208.50	$208.50
Purchase #6	$118.43	11.356%	$131.8789	$131.88	$131.90	$131.90
Purchase #7	$55.54	6.587%	$59.1984	$59.20	$59.20	$59.20
7 purchase totals =	$541.10		$591.9598	$591.96	$592.00	$592.00