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 $80.82   6.676%   $86.2155   $86.22   $86.20   $86.20  
  Purchase #2 $201.84   6.339%   $214.6346   $214.63   $214.65   $214.60  
  Purchase #3 $185.35   6.671%   $197.7147   $197.71   $197.70   $197.70  
  Purchase #4 $110.87   7.484%   $119.1675   $119.17   $119.15   $119.20  
  Purchase #5 $51.69   4.651%   $54.0941   $54.09   $54.10   $54.10  
  Purchase #6 $61.58   4.866%   $64.5765   $64.58   $64.60   $64.60  
  Purchase #7 $192.82   5.483%   $203.3923   $203.39   $203.40   $203.40  
  7 purchase totals = $884.97       $939.7952   $939.79   $939.80   $939.80