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	$124.72	10.338%	$137.6136	$137.61	$137.60	$137.60
Purchase #2	$87.54	11.243%	$97.3821	$97.38	$97.40	$97.40
Purchase #3	$113.78	3.131%	$117.3425	$117.34	$117.35	$117.30
Purchase #4	$87.68	11.184%	$97.4861	$97.49	$97.50	$97.50
Purchase #5	$39.81	9.221%	$43.4809	$43.48	$43.50	$43.50
Purchase #6	$83.39	9.411%	$91.2378	$91.24	$91.25	$91.20
Purchase #7	$78.95	4.202%	$82.2675	$82.27	$82.25	$82.30
7 purchase totals =	$615.87		$666.8105	$666.81	$666.85	$666.80