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 $246.70   6.344%   $262.3506   $262.35   $262.35   $262.40  
  Purchase #2 $227.75   10.524%   $251.7184   $251.72   $251.70   $251.70  
  Purchase #3 $56.43   10.717%   $62.4776   $62.48   $62.50   $62.50  
  Purchase #4 $28.78   6.201%   $30.5646   $30.56   $30.55   $30.60  
  Purchase #5 $137.74   5.539%   $145.3694   $145.37   $145.35   $145.40  
  Purchase #6 $165.77   11.410%   $184.6844   $184.68   $184.70   $184.70  
  Purchase #7 $69.37   10.472%   $76.6344   $76.63   $76.65   $76.60  
  7 purchase totals = $932.54       $1,013.7994   $1,013.79   $1,013.80   $1,013.90