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 $195.58   6.212%   $207.7294   $207.73   $207.75   $207.70  
  Purchase #2 $14.27   6.393%   $15.1823   $15.18   $15.20   $15.20  
  Purchase #3 $74.44   7.822%   $80.2627   $80.26   $80.25   $80.30  
  Purchase #4 $144.36   13.514%   $163.8688   $163.87   $163.85   $163.90  
  Purchase #5 $160.77   8.472%   $174.3904   $174.39   $174.40   $174.40  
  Purchase #6 $229.64   7.694%   $247.3085   $247.31   $247.30   $247.30  
  Purchase #7 $9.46   7.706%   $10.189   $10.19   $10.20   $10.20  
  7 purchase totals = $828.52       $898.9311   $898.93   $898.95   $899.00