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 $226.79   10.466%   $250.5258   $250.53   $250.55   $250.50  
  Purchase #2 $5.65   11.676%   $6.3097   $6.31   $6.30   $6.30  
  Purchase #3 $195.32   6.449%   $207.9162   $207.92   $207.90   $207.90  
  Purchase #4 $250.78   4.712%   $262.5968   $262.60   $262.60   $262.60  
  Purchase #5 $93.50   9.370%   $102.261   $102.26   $102.25   $102.30  
  Purchase #6 $163.36   8.174%   $176.713   $176.71   $176.70   $176.70  
  Purchase #7 $242.49   7.494%   $260.6622   $260.66   $260.65   $260.70  
  7 purchase totals = $1,177.89       $1,266.9847   $1,266.99   $1,266.95   $1,267.00