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 $60.78   4.828%   $63.7145   $63.71   $63.70   $63.70  
  Purchase #2 $65.91   7.108%   $70.5949   $70.59   $70.60   $70.60  
  Purchase #3 $137.55   12.790%   $155.1426   $155.14   $155.15   $155.10  
  Purchase #4 $126.36   7.223%   $135.487   $135.49   $135.50   $135.50  
  Purchase #5 $113.69   13.143%   $128.6323   $128.63   $128.65   $128.60  
  Purchase #6 $249.46   12.864%   $281.5505   $281.55   $281.55   $281.60  
  Purchase #7 $213.45   13.656%   $242.5987   $242.60   $242.60   $242.60  
  7 purchase totals = $967.20       $1,077.7205   $1,077.71   $1,077.75   $1,077.70