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	$132.30	3.760%	$137.2745	$137.27	$137.25	$137.30
Purchase #2	$91.78	10.690%	$101.5913	$101.59	$101.60	$101.60
Purchase #3	$77.30	7.123%	$82.8061	$82.81	$82.80	$82.80
Purchase #4	$127.69	7.587%	$137.3778	$137.38	$137.40	$137.40
Purchase #5	$187.77	5.176%	$197.489	$197.49	$197.50	$197.50
Purchase #6	$189.39	11.579%	$211.3195	$211.32	$211.30	$211.30
Purchase #7	$57.36	10.675%	$63.4832	$63.48	$63.50	$63.50
7 purchase totals =	$863.59		$931.3414	$931.34	$931.35	$931.40