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	$155.73	7.472%	$167.3661	$167.37	$167.35	$167.40
Purchase #2	$37.61	12.260%	$42.221	$42.22	$42.20	$42.20
Purchase #3	$84.56	11.139%	$93.9791	$93.98	$94.00	$94.00
Purchase #4	$85.42	9.366%	$93.4204	$93.42	$93.40	$93.40
Purchase #5	$135.66	4.160%	$141.3035	$141.30	$141.30	$141.30
Purchase #6	$35.32	13.264%	$40.0048	$40.00	$40.00	$40.00
Purchase #7	$74.51	10.725%	$82.5012	$82.50	$82.50	$82.50
7 purchase totals =	$608.81		$660.7961	$660.79	$660.75	$660.80