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 $112.87   12.571%   $127.0589   $127.06   $127.05   $127.10  
  Purchase #2 $239.50   8.253%   $259.2659   $259.27   $259.25   $259.30  
  Purchase #3 $159.45   11.114%   $177.1713   $177.17   $177.15   $177.20  
  Purchase #4 $186.57   5.389%   $196.6243   $196.62   $196.60   $196.60  
  Purchase #5 $41.30   6.840%   $44.1249   $44.12   $44.10   $44.10  
  Purchase #6 $221.48   13.407%   $251.1738   $251.17   $251.15   $251.20  
  Purchase #7 $191.55   10.189%   $211.067   $211.07   $211.05   $211.10  
  7 purchase totals = $1,152.72       $1,266.4861   $1,266.48   $1,266.35   $1,266.60