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	$67.56	6.851%	$72.1885	$72.19	$72.20	$72.20
Purchase #2	$125.56	13.425%	$142.4164	$142.42	$142.40	$142.40
Purchase #3	$29.52	5.259%	$31.0725	$31.07	$31.05	$31.10
Purchase #4	$89.31	10.680%	$98.8483	$98.85	$98.85	$98.80
Purchase #5	$167.60	13.822%	$190.7657	$190.77	$190.75	$190.80
Purchase #6	$170.75	12.742%	$192.507	$192.51	$192.50	$192.50
Purchase #7	$214.86	11.329%	$239.2015	$239.20	$239.20	$239.20
7 purchase totals =	$865.16		$966.9999	$967.01	$966.95	$967.00