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 $159.27   9.723%   $174.7558   $174.76   $174.75   $174.80  
  Purchase #2 $238.78   9.859%   $262.3213   $262.32   $262.30   $262.30  
  Purchase #3 $226.49   6.311%   $240.7838   $240.78   $240.80   $240.80  
  Purchase #4 $58.71   4.770%   $61.5105   $61.51   $61.50   $61.50  
  Purchase #5 $49.31   5.264%   $51.9057   $51.91   $51.90   $51.90  
  Purchase #6 $200.38   10.133%   $220.6845   $220.68   $220.70   $220.70  
  Purchase #7 $177.57   7.706%   $191.2535   $191.25   $191.25   $191.30  
  7 purchase totals = $1,110.51       $1,203.2151   $1,203.21   $1,203.20   $1,203.30