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 $244.87   8.157%   $264.844   $264.84   $264.85   $264.80  
  Purchase #2 $40.93   8.541%   $44.4258   $44.43   $44.45   $44.40  
  Purchase #3 $69.58   7.284%   $74.6482   $74.65   $74.65   $74.60  
  Purchase #4 $132.49   7.807%   $142.8335   $142.83   $142.85   $142.80  
  Purchase #5 $176.95   5.443%   $186.5814   $186.58   $186.60   $186.60  
  Purchase #6 $15.54   7.189%   $16.6572   $16.66   $16.65   $16.70  
  Purchase #7 $54.81   5.276%   $57.7018   $57.70   $57.70   $57.70  
  7 purchase totals = $735.17       $787.6919   $787.69   $787.75   $787.60