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 $72.65   3.576%   $75.248   $75.25   $75.25   $75.20  
  Purchase #2 $64.82   6.249%   $68.8706   $68.87   $68.85   $68.90  
  Purchase #3 $191.54   3.676%   $198.581   $198.58   $198.60   $198.60  
  Purchase #4 $16.84   5.521%   $17.7697   $17.77   $17.75   $17.80  
  Purchase #5 $196.25   8.639%   $213.204   $213.20   $213.20   $213.20  
  Purchase #6 $242.45   6.524%   $258.2674   $258.27   $258.25   $258.30  
  Purchase #7 $78.36   6.273%   $83.2755   $83.28   $83.30   $83.30  
  7 purchase totals = $862.91       $915.2162   $915.22   $915.20   $915.30