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 $22.63   8.839%   $24.6303   $24.63   $24.65   $24.60  
  Purchase #2 $148.96   11.130%   $165.5392   $165.54   $165.55   $165.50  
  Purchase #3 $137.66   5.318%   $144.9808   $144.98   $145.00   $145.00  
  Purchase #4 $161.92   8.239%   $175.2606   $175.26   $175.25   $175.30  
  Purchase #5 $187.70   10.368%   $207.1607   $207.16   $207.15   $207.20  
  Purchase #6 $142.31   8.597%   $154.5444   $154.54   $154.55   $154.50  
  Purchase #7 $139.38   3.428%   $144.1579   $144.16   $144.15   $144.20  
  7 purchase totals = $940.56       $1,016.2739   $1,016.27   $1,016.30   $1,016.30