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 $146.53   7.126%   $156.9717   $156.97   $156.95   $157.00  
  Purchase #2 $95.47   9.843%   $104.8671   $104.87   $104.85   $104.90  
  Purchase #3 $60.62   10.527%   $67.0015   $67.00   $67.00   $67.00  
  Purchase #4 $73.41   7.452%   $78.8805   $78.88   $78.90   $78.90  
  Purchase #5 $202.34   4.610%   $211.6679   $211.67   $211.65   $211.70  
  Purchase #6 $97.48   13.139%   $110.2879   $110.29   $110.30   $110.30  
  Purchase #7 $182.48   7.608%   $196.3631   $196.36   $196.35   $196.40  
  7 purchase totals = $858.33       $926.0397   $926.04   $926.00   $926.20