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	$83.88	9.226%	$91.6188	$91.62	$91.60	$91.60
Purchase #2	$80.97	11.646%	$90.3998	$90.40	$90.40	$90.40
Purchase #3	$230.36	4.392%	$240.4774	$240.48	$240.50	$240.50
Purchase #4	$204.47	7.641%	$220.0936	$220.09	$220.10	$220.10
Purchase #5	$190.44	9.600%	$208.7222	$208.72	$208.70	$208.70
Purchase #6	$13.40	6.804%	$14.3117	$14.31	$14.30	$14.30
Purchase #7	$83.84	7.731%	$90.3217	$90.32	$90.30	$90.30
7 purchase totals =	$887.36		$955.9452	$955.94	$955.90	$955.90