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 $76.95   8.386%   $83.403   $83.40   $83.40   $83.40  
  Purchase #2 $146.76   13.103%   $165.99   $165.99   $166.00   $166.00  
  Purchase #3 $205.89   3.681%   $213.4688   $213.47   $213.45   $213.50  
  Purchase #4 $24.45   12.759%   $27.5696   $27.57   $27.55   $27.60  
  Purchase #5 $99.56   3.737%   $103.2806   $103.28   $103.30   $103.30  
  Purchase #6 $127.51   6.320%   $135.5686   $135.57   $135.55   $135.60  
  Purchase #7 $29.62   3.546%   $30.6703   $30.67   $30.65   $30.70  
  7 purchase totals = $710.74       $759.9509   $759.95   $759.90   $760.10