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 $164.45   7.796%   $177.2705   $177.27   $177.25   $177.30  
  Purchase #2 $65.69   6.108%   $69.7023   $69.70   $69.70   $69.70  
  Purchase #3 $68.38   6.742%   $72.9902   $72.99   $73.00   $73.00  
  Purchase #4 $165.62   13.810%   $188.4921   $188.49   $188.50   $188.50  
  Purchase #5 $196.30   5.354%   $206.8099   $206.81   $206.80   $206.80  
  Purchase #6 $249.99   12.727%   $281.8062   $281.81   $281.80   $281.80  
  Purchase #7 $34.61   7.387%   $37.1666   $37.17   $37.15   $37.20  
  7 purchase totals = $945.04       $1,034.2378   $1,034.24   $1,034.20   $1,034.30