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 $61.64   8.594%   $66.9373   $66.94   $66.95   $66.90  
  Purchase #2 $182.47   6.455%   $194.2484   $194.25   $194.25   $194.20  
  Purchase #3 $165.84   5.734%   $175.3493   $175.35   $175.35   $175.30  
  Purchase #4 $35.92   10.605%   $39.7293   $39.73   $39.75   $39.70  
  Purchase #5 $97.50   8.644%   $105.9279   $105.93   $105.95   $105.90  
  Purchase #6 $26.69   12.397%   $29.9988   $30.00   $30.00   $30.00  
  Purchase #7 $233.75   7.171%   $250.5122   $250.51   $250.50   $250.50  
  7 purchase totals = $803.81       $862.7032   $862.71   $862.75   $862.50