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 $227.95   9.799%   $250.2868   $250.29   $250.30   $250.30  
  Purchase #2 $73.94   3.704%   $76.6787   $76.68   $76.70   $76.70  
  Purchase #3 $192.31   4.405%   $200.7813   $200.78   $200.80   $200.80  
  Purchase #4 $22.91   3.622%   $23.7398   $23.74   $23.75   $23.70  
  Purchase #5 $77.67   5.411%   $81.8727   $81.87   $81.85   $81.90  
  Purchase #6 $209.26   12.678%   $235.79   $235.79   $235.80   $235.80  
  Purchase #7 $246.84   11.628%   $275.5426   $275.54   $275.55   $275.50  
  7 purchase totals = $1,050.88       $1,144.6919   $1,144.69   $1,144.75   $1,144.70