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 $114.62   9.648%   $125.6785   $125.68   $125.70   $125.70  
  Purchase #2 $202.89   7.396%   $217.8957   $217.90   $217.90   $217.90  
  Purchase #3 $54.66   13.317%   $61.9391   $61.94   $61.95   $61.90  
  Purchase #4 $150.56   9.466%   $164.812   $164.81   $164.80   $164.80  
  Purchase #5 $15.98   11.200%   $17.7698   $17.77   $17.75   $17.80  
  Purchase #6 $47.32   7.471%   $50.8553   $50.86   $50.85   $50.90  
  Purchase #7 $98.26   5.844%   $104.0023   $104.00   $104.00   $104.00  
  7 purchase totals = $684.29       $742.9527   $742.96   $742.95   $743.00