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 $66.71   13.443%   $75.6778   $75.68   $75.70   $75.70  
  Purchase #2 $237.54   10.758%   $263.0946   $263.09   $263.10   $263.10  
  Purchase #3 $76.83   9.830%   $84.3824   $84.38   $84.40   $84.40  
  Purchase #4 $203.27   5.869%   $215.1999   $215.20   $215.20   $215.20  
  Purchase #5 $127.76   13.289%   $144.738   $144.74   $144.75   $144.70  
  Purchase #6 $172.27   9.165%   $188.0585   $188.06   $188.05   $188.10  
  Purchase #7 $234.86   8.558%   $254.9593   $254.96   $254.95   $255.00  
  7 purchase totals = $1,119.24       $1,226.1105   $1,226.11   $1,226.15   $1,226.20