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 $62.36   5.853%   $66.0099   $66.01   $66.00   $66.00  
  Purchase #2 $140.67   12.209%   $157.8444   $157.84   $157.85   $157.80  
  Purchase #3 $173.32   3.118%   $178.7241   $178.72   $178.70   $178.70  
  Purchase #4 $100.76   8.495%   $109.3196   $109.32   $109.30   $109.30  
  Purchase #5 $151.99   6.108%   $161.2735   $161.27   $161.25   $161.30  
  Purchase #6 $194.71   5.155%   $204.7473   $204.75   $204.75   $204.70  
  Purchase #7 $7.58   13.568%   $8.6085   $8.61   $8.60   $8.60  
  7 purchase totals = $831.39       $886.5273   $886.52   $886.45   $886.40