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 $46.65   6.391%   $49.6314   $49.63   $49.65   $49.60  
  Purchase #2 $165.41   7.724%   $178.1863   $178.19   $178.20   $178.20  
  Purchase #3 $231.80   11.122%   $257.5808   $257.58   $257.60   $257.60  
  Purchase #4 $225.50   7.645%   $242.7395   $242.74   $242.75   $242.70  
  Purchase #5 $52.51   12.526%   $59.0874   $59.09   $59.10   $59.10  
  Purchase #6 $170.68   11.472%   $190.2604   $190.26   $190.25   $190.30  
  Purchase #7 $15.70   11.644%   $17.5281   $17.53   $17.55   $17.50  
  7 purchase totals = $908.25       $995.0139   $995.02   $995.10   $995.00