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 $61.62   3.528%   $63.794   $63.79   $63.80   $63.80  
  Purchase #2 $32.38   8.838%   $35.2417   $35.24   $35.25   $35.20  
  Purchase #3 $37.90   3.315%   $39.1564   $39.16   $39.15   $39.20  
  Purchase #4 $173.73   9.690%   $190.5644   $190.56   $190.55   $190.60  
  Purchase #5 $188.73   9.186%   $206.0667   $206.07   $206.05   $206.10  
  Purchase #6 $173.49   13.167%   $196.3334   $196.33   $196.35   $196.30  
  Purchase #7 $147.94   11.669%   $165.2031   $165.20   $165.20   $165.20  
  7 purchase totals = $815.79       $896.3597   $896.35   $896.35   $896.40