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 $24.55   10.160%   $27.0443   $27.04   $27.05   $27.00  
  Purchase #2 $44.68   11.234%   $49.6994   $49.70   $49.70   $49.70  
  Purchase #3 $91.70   10.835%   $101.6357   $101.64   $101.65   $101.60  
  Purchase #4 $104.94   6.754%   $112.0276   $112.03   $112.05   $112.00  
  Purchase #5 $178.63   5.547%   $188.5386   $188.54   $188.55   $188.50  
  Purchase #6 $205.66   8.184%   $222.4912   $222.49   $222.50   $222.50  
  Purchase #7 $135.83   3.514%   $140.6031   $140.60   $140.60   $140.60  
  7 purchase totals = $785.99       $842.0399   $842.04   $842.10   $841.90