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 $60.37   8.256%   $65.3541   $65.35   $65.35   $65.40  
  Purchase #2 $207.65   13.265%   $235.1948   $235.19   $235.20   $235.20  
  Purchase #3 $23.36   6.603%   $24.9025   $24.90   $24.90   $24.90  
  Purchase #4 $49.89   6.691%   $53.2281   $53.23   $53.25   $53.20  
  Purchase #5 $152.70   11.296%   $169.949   $169.95   $169.95   $169.90  
  Purchase #6 $136.30   12.197%   $152.9245   $152.92   $152.90   $152.90  
  Purchase #7 $221.32   5.625%   $233.7693   $233.77   $233.75   $233.80  
  7 purchase totals = $851.59       $935.3223   $935.31   $935.30   $935.30