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 $135.49   12.132%   $151.9276   $151.93   $151.95   $151.90  
  Purchase #2 $221.79   13.755%   $252.2972   $252.30   $252.30   $252.30  
  Purchase #3 $86.30   13.699%   $98.1222   $98.12   $98.10   $98.10  
  Purchase #4 $201.56   6.524%   $214.7098   $214.71   $214.70   $214.70  
  Purchase #5 $139.63   8.348%   $151.2863   $151.29   $151.30   $151.30  
  Purchase #6 $51.50   13.731%   $58.5715   $58.57   $58.55   $58.60  
  Purchase #7 $248.87   11.330%   $277.067   $277.07   $277.05   $277.10  
  7 purchase totals = $1,085.14       $1,203.9816   $1,203.99   $1,203.95   $1,204.00