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	$125.43	11.402%	$139.7315	$139.73	$139.75	$139.70
Purchase #2	$140.39	8.170%	$151.8599	$151.86	$151.85	$151.90
Purchase #3	$10.41	5.762%	$11.0098	$11.01	$11.00	$11.00
Purchase #4	$171.25	5.630%	$180.8914	$180.89	$180.90	$180.90
Purchase #5	$198.86	13.658%	$226.0203	$226.02	$226.00	$226.00
Purchase #6	$176.89	13.563%	$200.8816	$200.88	$200.90	$200.90
Purchase #7	$15.34	13.557%	$17.4196	$17.42	$17.40	$17.40
7 purchase totals =	$838.57		$927.8141	$927.81	$927.80	$927.80