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	$21.29	5.156%	$22.3877	$22.39	$22.40	$22.40
Purchase #2	$56.47	12.636%	$63.6055	$63.61	$63.60	$63.60
Purchase #3	$80.25	9.110%	$87.5608	$87.56	$87.55	$87.60
Purchase #4	$80.83	5.780%	$85.502	$85.50	$85.50	$85.50
Purchase #5	$43.96	6.392%	$46.7699	$46.77	$46.75	$46.80
Purchase #6	$29.64	13.631%	$33.6802	$33.68	$33.70	$33.70
Purchase #7	$240.31	12.305%	$269.8801	$269.88	$269.90	$269.90
7 purchase totals =	$552.75		$609.3862	$609.39	$609.40	$609.50