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 $111.68   6.647%   $119.1034   $119.10   $119.10   $119.10  
  Purchase #2 $246.53   5.329%   $259.6676   $259.67   $259.65   $259.70  
  Purchase #3 $73.62   13.745%   $83.7391   $83.74   $83.75   $83.70  
  Purchase #4 $127.64   6.326%   $135.7145   $135.71   $135.70   $135.70  
  Purchase #5 $163.74   11.617%   $182.7617   $182.76   $182.75   $182.80  
  Purchase #6 $249.96   6.167%   $265.375   $265.38   $265.40   $265.40  
  Purchase #7 $162.57   7.256%   $174.3661   $174.37   $174.35   $174.40  
  7 purchase totals = $1,135.74       $1,220.7274   $1,220.73   $1,220.70   $1,220.80