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 $21.40   3.662%   $22.1837   $22.18   $22.20   $22.20  
  Purchase #2 $30.84   5.314%   $32.4788   $32.48   $32.50   $32.50  
  Purchase #3 $134.68   8.805%   $146.5386   $146.54   $146.55   $146.50  
  Purchase #4 $167.72   4.379%   $175.0645   $175.06   $175.05   $175.10  
  Purchase #5 $209.57   5.166%   $220.3964   $220.40   $220.40   $220.40  
  Purchase #6 $229.74   8.796%   $249.9479   $249.95   $249.95   $249.90  
  Purchase #7 $86.90   8.704%   $94.4638   $94.46   $94.45   $94.50  
  7 purchase totals = $880.85       $941.0737   $941.07   $941.10   $941.10