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 $15.53   13.526%   $17.6306   $17.63   $17.65   $17.60  
  Purchase #2 $164.73   6.202%   $174.9466   $174.95   $174.95   $174.90  
  Purchase #3 $144.57   13.277%   $163.7646   $163.76   $163.75   $163.80  
  Purchase #4 $119.29   11.227%   $132.6827   $132.68   $132.70   $132.70  
  Purchase #5 $202.51   3.539%   $209.6768   $209.68   $209.70   $209.70  
  Purchase #6 $11.68   4.777%   $12.238   $12.24   $12.25   $12.20  
  Purchase #7 $127.26   9.203%   $138.9717   $138.97   $138.95   $139.00  
  7 purchase totals = $785.57       $849.9110   $849.91   $849.95   $849.90