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 $42.59   11.808%   $47.619   $47.62   $47.60   $47.60  
  Purchase #2 $235.34   10.662%   $260.432   $260.43   $260.45   $260.40  
  Purchase #3 $205.63   10.331%   $226.8736   $226.87   $226.85   $226.90  
  Purchase #4 $24.66   7.873%   $26.6015   $26.60   $26.60   $26.60  
  Purchase #5 $83.62   7.264%   $89.6942   $89.69   $89.70   $89.70  
  Purchase #6 $38.83   4.211%   $40.4651   $40.47   $40.45   $40.50  
  Purchase #7 $241.94   3.380%   $250.1176   $250.12   $250.10   $250.10  
  7 purchase totals = $872.61       $941.8030   $941.80   $941.75   $941.80