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	$150.61	3.771%	$156.2895	$156.29	$156.30	$156.30
Purchase #2	$227.98	8.570%	$247.5179	$247.52	$247.50	$247.50
Purchase #3	$63.43	4.116%	$66.0408	$66.04	$66.05	$66.00
Purchase #4	$203.75	10.840%	$225.8365	$225.84	$225.85	$225.80
Purchase #5	$27.83	7.440%	$29.9006	$29.90	$29.90	$29.90
Purchase #6	$184.54	6.196%	$195.9741	$195.97	$195.95	$196.00
Purchase #7	$38.67	10.806%	$42.8487	$42.85	$42.85	$42.80
7 purchase totals =	$896.81		$964.4081	$964.41	$964.40	$964.30