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 $187.99   10.798%   $208.2892   $208.29   $208.30   $208.30  
  Purchase #2 $121.92   4.271%   $127.1272   $127.13   $127.15   $127.10  
  Purchase #3 $66.80   12.419%   $75.0959   $75.10   $75.10   $75.10  
  Purchase #4 $203.27   11.239%   $226.1155   $226.12   $226.10   $226.10  
  Purchase #5 $209.70   5.361%   $220.942   $220.94   $220.95   $220.90  
  Purchase #6 $40.70   4.687%   $42.6076   $42.61   $42.60   $42.60  
  Purchase #7 $146.97   13.686%   $167.0843   $167.08   $167.10   $167.10  
  7 purchase totals = $977.35       $1,067.2617   $1,067.27   $1,067.30   $1,067.20