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 $63.50   8.143%   $68.6708   $68.67   $68.65   $68.70  
  Purchase #2 $243.63   8.791%   $265.0475   $265.05   $265.05   $265.00  
  Purchase #3 $244.90   5.251%   $257.7597   $257.76   $257.75   $257.80  
  Purchase #4 $199.66   13.835%   $227.283   $227.28   $227.30   $227.30  
  Purchase #5 $136.33   3.215%   $140.713   $140.71   $140.70   $140.70  
  Purchase #6 $127.46   13.681%   $144.8978   $144.90   $144.90   $144.90  
  Purchase #7 $227.50   13.691%   $258.647   $258.65   $258.65   $258.60  
  7 purchase totals = $1,242.98       $1,363.0188   $1,363.02   $1,363.00   $1,363.00