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 $57.67   10.423%   $63.6809   $63.68   $63.70   $63.70  
  Purchase #2 $212.88   12.587%   $239.6752   $239.68   $239.70   $239.70  
  Purchase #3 $8.88   11.388%   $9.8913   $9.89   $9.90   $9.90  
  Purchase #4 $242.71   7.431%   $260.7458   $260.75   $260.75   $260.70  
  Purchase #5 $49.30   9.736%   $54.0998   $54.10   $54.10   $54.10  
  Purchase #6 $167.63   7.151%   $179.6172   $179.62   $179.60   $179.60  
  Purchase #7 $219.92   3.868%   $228.4265   $228.43   $228.45   $228.40  
  7 purchase totals = $958.99       $1,036.1367   $1,036.15   $1,036.20   $1,036.10