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 $40.63   7.532%   $43.6903   $43.69   $43.70   $43.70  
  Purchase #2 $231.83   12.151%   $259.9997   $260.00   $260.00   $260.00  
  Purchase #3 $111.66   7.609%   $120.1562   $120.16   $120.15   $120.20  
  Purchase #4 $133.59   12.141%   $149.8092   $149.81   $149.80   $149.80  
  Purchase #5 $107.32   13.247%   $121.5367   $121.54   $121.55   $121.50  
  Purchase #6 $183.42   5.602%   $193.6952   $193.70   $193.70   $193.70  
  Purchase #7 $78.82   7.800%   $84.968   $84.97   $84.95   $85.00  
  7 purchase totals = $887.27       $973.8553   $973.87   $973.85   $973.90