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 $55.86   4.871%   $58.5809   $58.58   $58.60   $58.60  
  Purchase #2 $86.92   13.224%   $98.4143   $98.41   $98.40   $98.40  
  Purchase #3 $182.75   11.195%   $203.2089   $203.21   $203.20   $203.20  
  Purchase #4 $165.32   6.244%   $175.6426   $175.64   $175.65   $175.60  
  Purchase #5 $18.80   5.425%   $19.8199   $19.82   $19.80   $19.80  
  Purchase #6 $213.88   11.657%   $238.812   $238.81   $238.80   $238.80  
  Purchase #7 $139.94   12.381%   $157.266   $157.27   $157.25   $157.30  
  7 purchase totals = $863.47       $951.7446   $951.74   $951.70   $951.70