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 $176.33   11.849%   $197.2233   $197.22   $197.20   $197.20  
  Purchase #2 $44.76   4.141%   $46.6135   $46.61   $46.60   $46.60  
  Purchase #3 $21.57   7.383%   $23.1625   $23.16   $23.15   $23.20  
  Purchase #4 $127.86   8.333%   $138.5146   $138.51   $138.50   $138.50  
  Purchase #5 $161.40   8.573%   $175.2368   $175.24   $175.25   $175.20  
  Purchase #6 $135.95   13.712%   $154.5915   $154.59   $154.60   $154.60  
  Purchase #7 $120.89   4.362%   $126.1632   $126.16   $126.15   $126.20  
  7 purchase totals = $788.76       $861.5054   $861.49   $861.45   $861.50