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 $125.88   4.779%   $131.8958   $131.90   $131.90   $131.90  
  Purchase #2 $211.41   4.446%   $220.8093   $220.81   $220.80   $220.80  
  Purchase #3 $30.27   6.587%   $32.2639   $32.26   $32.25   $32.30  
  Purchase #4 $198.46   4.576%   $207.5415   $207.54   $207.55   $207.50  
  Purchase #5 $81.86   6.146%   $86.8911   $86.89   $86.90   $86.90  
  Purchase #6 $86.98   6.134%   $92.3154   $92.32   $92.30   $92.30  
  Purchase #7 $6.97   4.103%   $7.256   $7.26   $7.25   $7.30  
  7 purchase totals = $741.83       $778.9730   $778.98   $778.95   $779.00