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	$33.56	11.519%	$37.4258	$37.43	$37.45	$37.40
Purchase #2	$213.26	6.535%	$227.1965	$227.20	$227.20	$227.20
Purchase #3	$30.83	8.285%	$33.3843	$33.38	$33.40	$33.40
Purchase #4	$125.28	12.467%	$140.8987	$140.90	$140.90	$140.90
Purchase #5	$91.62	10.789%	$101.5049	$101.50	$101.50	$101.50
Purchase #6	$113.62	4.396%	$118.6147	$118.61	$118.60	$118.60
Purchase #7	$249.64	13.866%	$284.2551	$284.26	$284.25	$284.30
7 purchase totals =	$857.81		$943.2800	$943.28	$943.30	$943.30