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	$28.32	10.530%	$31.3021	$31.30	$31.30	$31.30
Purchase #2	$91.75	7.824%	$98.9285	$98.93	$98.95	$98.90
Purchase #3	$116.90	4.147%	$121.7478	$121.75	$121.75	$121.70
Purchase #4	$16.59	5.697%	$17.5351	$17.54	$17.55	$17.50
Purchase #5	$83.84	4.371%	$87.5046	$87.50	$87.50	$87.50
Purchase #6	$150.71	9.192%	$164.5633	$164.56	$164.55	$164.60
Purchase #7	$129.98	12.209%	$145.8493	$145.85	$145.85	$145.80
7 purchase totals =	$618.09		$667.4307	$667.43	$667.45	$667.30