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 $214.85   9.808%   $235.9225   $235.92   $235.90   $235.90  
  Purchase #2 $121.40   11.728%   $135.6378   $135.64   $135.65   $135.60  
  Purchase #3 $110.60   6.462%   $117.747   $117.75   $117.75   $117.70  
  Purchase #4 $125.35   6.295%   $133.2408   $133.24   $133.25   $133.20  
  Purchase #5 $63.87   13.670%   $72.601   $72.60   $72.60   $72.60  
  Purchase #6 $102.44   3.678%   $106.2077   $106.21   $106.20   $106.20  
  Purchase #7 $93.63   5.285%   $98.5783   $98.58   $98.60   $98.60  
  7 purchase totals = $832.14       $899.9351   $899.94   $899.95   $899.80