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 $235.64   10.323%   $259.9651   $259.97   $259.95   $260.00  
  Purchase #2 $182.46   5.359%   $192.238   $192.24   $192.25   $192.20  
  Purchase #3 $236.88   9.327%   $258.9738   $258.97   $258.95   $259.00  
  Purchase #4 $236.65   5.825%   $250.4349   $250.43   $250.45   $250.40  
  Purchase #5 $58.85   6.447%   $62.6441   $62.64   $62.65   $62.60  
  Purchase #6 $189.93   8.264%   $205.6258   $205.63   $205.65   $205.60  
  Purchase #7 $19.47   9.425%   $21.305   $21.31   $21.30   $21.30  
  7 purchase totals = $1,159.88       $1,251.1867   $1,251.19   $1,251.20   $1,251.10