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 $143.88   13.274%   $162.9786   $162.98   $163.00   $163.00  
  Purchase #2 $132.44   5.448%   $139.6553   $139.66   $139.65   $139.70  
  Purchase #3 $146.53   6.739%   $156.4047   $156.40   $156.40   $156.40  
  Purchase #4 $235.46   6.150%   $249.9408   $249.94   $249.95   $249.90  
  Purchase #5 $33.90   10.420%   $37.4324   $37.43   $37.45   $37.40  
  Purchase #6 $182.54   10.259%   $201.2668   $201.27   $201.25   $201.30  
  Purchase #7 $58.69   8.506%   $63.6822   $63.68   $63.70   $63.70  
  7 purchase totals = $933.44       $1,011.3608   $1,011.36   $1,011.40   $1,011.40