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 $34.48   13.550%   $39.152   $39.15   $39.15   $39.20  
  Purchase #2 $197.95   4.368%   $206.5965   $206.60   $206.60   $206.60  
  Purchase #3 $210.38   5.129%   $221.1704   $221.17   $221.15   $221.20  
  Purchase #4 $11.51   3.779%   $11.945   $11.95   $11.95   $11.90  
  Purchase #5 $216.66   11.577%   $241.7427   $241.74   $241.75   $241.70  
  Purchase #6 $50.83   3.445%   $52.5811   $52.58   $52.60   $52.60  
  Purchase #7 $118.50   3.171%   $122.2576   $122.26   $122.25   $122.30  
  7 purchase totals = $840.31       $895.4453   $895.45   $895.45   $895.50