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 $56.88   8.285%   $61.5925   $61.59   $61.60   $61.60  
  Purchase #2 $110.36   10.846%   $122.3296   $122.33   $122.35   $122.30  
  Purchase #3 $235.71   11.270%   $262.2745   $262.27   $262.25   $262.30  
  Purchase #4 $64.73   7.239%   $69.4158   $69.42   $69.40   $69.40  
  Purchase #5 $190.89   7.132%   $204.5043   $204.50   $204.50   $204.50  
  Purchase #6 $107.62   12.763%   $121.3555   $121.36   $121.35   $121.40  
  Purchase #7 $123.74   8.217%   $133.9077   $133.91   $133.90   $133.90  
  7 purchase totals = $889.93       $975.3799   $975.38   $975.35   $975.40