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 $215.26   11.837%   $240.7403   $240.74   $240.75   $240.70  
  Purchase #2 $95.69   12.845%   $107.9814   $107.98   $108.00   $108.00  
  Purchase #3 $178.49   5.119%   $187.6269   $187.63   $187.65   $187.60  
  Purchase #4 $134.83   10.281%   $148.6919   $148.69   $148.70   $148.70  
  Purchase #5 $170.64   13.139%   $193.0604   $193.06   $193.05   $193.10  
  Purchase #6 $139.74   6.459%   $148.7658   $148.77   $148.75   $148.80  
  Purchase #7 $46.93   5.737%   $49.6224   $49.62   $49.60   $49.60  
  7 purchase totals = $981.58       $1,076.4891   $1,076.49   $1,076.50   $1,076.50