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 $61.50   6.435%   $65.4575   $65.46   $65.45   $65.50  
  Purchase #2 $211.38   11.599%   $235.898   $235.90   $235.90   $235.90  
  Purchase #3 $211.63   11.833%   $236.6722   $236.67   $236.65   $236.70  
  Purchase #4 $47.66   8.687%   $51.8002   $51.80   $51.80   $51.80  
  Purchase #5 $180.55   7.385%   $193.8836   $193.88   $193.90   $193.90  
  Purchase #6 $77.80   5.287%   $81.9133   $81.91   $81.90   $81.90  
  Purchase #7 $146.82   7.691%   $158.1119   $158.11   $158.10   $158.10  
  7 purchase totals = $937.34       $1,023.7367   $1,023.73   $1,023.70   $1,023.80