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 $87.53   6.779%   $93.4637   $93.46   $93.45   $93.50  
  Purchase #2 $116.68   4.258%   $121.6482   $121.65   $121.65   $121.60  
  Purchase #3 $122.25   10.675%   $135.3002   $135.30   $135.30   $135.30  
  Purchase #4 $24.88   5.619%   $26.278   $26.28   $26.30   $26.30  
  Purchase #5 $76.85   4.592%   $80.379   $80.38   $80.40   $80.40  
  Purchase #6 $142.34   8.341%   $154.2126   $154.21   $154.20   $154.20  
  Purchase #7 $38.48   5.114%   $40.4479   $40.45   $40.45   $40.40  
  7 purchase totals = $609.01       $651.7296   $651.73   $651.75   $651.70