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 $62.32   7.395%   $66.9286   $66.93   $66.95   $66.90  
  Purchase #2 $208.26   11.617%   $232.4536   $232.45   $232.45   $232.50  
  Purchase #3 $35.95   9.126%   $39.2308   $39.23   $39.25   $39.20  
  Purchase #4 $220.32   3.807%   $228.7076   $228.71   $228.70   $228.70  
  Purchase #5 $24.86   5.396%   $26.2014   $26.20   $26.20   $26.20  
  Purchase #6 $179.26   7.808%   $193.2566   $193.26   $193.25   $193.30  
  Purchase #7 $220.61   7.557%   $237.2815   $237.28   $237.30   $237.30  
  7 purchase totals = $951.58       $1,024.0601   $1,024.06   $1,024.10   $1,024.10