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 $240.86   8.678%   $261.7618   $261.76   $261.75   $261.80  
  Purchase #2 $222.72   3.114%   $229.6555   $229.66   $229.65   $229.70  
  Purchase #3 $244.42   10.440%   $269.9374   $269.94   $269.95   $269.90  
  Purchase #4 $158.30   5.695%   $167.3152   $167.32   $167.30   $167.30  
  Purchase #5 $116.65   12.709%   $131.475   $131.48   $131.50   $131.50  
  Purchase #6 $212.48   8.411%   $230.3517   $230.35   $230.35   $230.40  
  Purchase #7 $54.75   10.732%   $60.6258   $60.63   $60.65   $60.60  
  7 purchase totals = $1,250.18       $1,351.1224   $1,351.14   $1,351.15   $1,351.20