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 $218.62   12.533%   $246.0196   $246.02   $246.00   $246.00  
  Purchase #2 $72.69   4.788%   $76.1704   $76.17   $76.15   $76.20  
  Purchase #3 $68.50   12.485%   $77.0522   $77.05   $77.05   $77.10  
  Purchase #4 $153.95   8.269%   $166.6801   $166.68   $166.70   $166.70  
  Purchase #5 $187.88   7.599%   $202.157   $202.16   $202.15   $202.20  
  Purchase #6 $32.56   8.185%   $35.225   $35.23   $35.25   $35.20  
  Purchase #7 $151.93   10.798%   $168.3354   $168.34   $168.35   $168.30  
  7 purchase totals = $886.13       $971.6397   $971.65   $971.65   $971.70