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 $155.46   9.181%   $169.7328   $169.73   $169.75   $169.70  
  Purchase #2 $72.66   4.561%   $75.974   $75.97   $75.95   $76.00  
  Purchase #3 $219.34   8.609%   $238.223   $238.22   $238.20   $238.20  
  Purchase #4 $239.37   10.280%   $263.9772   $263.98   $264.00   $264.00  
  Purchase #5 $49.84   13.312%   $56.4747   $56.47   $56.45   $56.50  
  Purchase #6 $152.92   12.677%   $172.3057   $172.31   $172.30   $172.30  
  Purchase #7 $250.45   4.218%   $261.014   $261.01   $261.00   $261.00  
  7 purchase totals = $1,140.04       $1,237.7014   $1,237.69   $1,237.65   $1,237.70