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 $224.67   7.726%   $242.028   $242.03   $242.05   $242.00  
  Purchase #2 $167.60   12.626%   $188.7612   $188.76   $188.75   $188.80  
  Purchase #3 $228.81   5.564%   $241.541   $241.54   $241.55   $241.50  
  Purchase #4 $167.68   6.784%   $179.0554   $179.06   $179.05   $179.10  
  Purchase #5 $78.78   13.735%   $89.6004   $89.60   $89.60   $89.60  
  Purchase #6 $232.54   10.358%   $256.6265   $256.63   $256.65   $256.60  
  Purchase #7 $66.78   12.482%   $75.1155   $75.12   $75.10   $75.10  
  7 purchase totals = $1,166.86       $1,272.7280   $1,272.74   $1,272.75   $1,272.70