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 $55.74   9.455%   $61.0102   $61.01   $61.00   $61.00  
  Purchase #2 $163.35   7.670%   $175.8789   $175.88   $175.90   $175.90  
  Purchase #3 $63.25   5.181%   $66.527   $66.53   $66.55   $66.50  
  Purchase #4 $146.43   5.776%   $154.8878   $154.89   $154.90   $154.90  
  Purchase #5 $52.27   8.863%   $56.9027   $56.90   $56.90   $56.90  
  Purchase #6 $161.79   6.432%   $172.1963   $172.20   $172.20   $172.20  
  Purchase #7 $209.75   8.297%   $227.153   $227.15   $227.15   $227.20  
  7 purchase totals = $852.58       $914.5559   $914.56   $914.60   $914.60