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 $68.55   8.819%   $74.5954   $74.60   $74.60   $74.60  
  Purchase #2 $131.82   5.189%   $138.6601   $138.66   $138.65   $138.70  
  Purchase #3 $248.86   6.516%   $265.0757   $265.08   $265.10   $265.10  
  Purchase #4 $53.39   7.548%   $57.4199   $57.42   $57.40   $57.40  
  Purchase #5 $119.44   4.411%   $124.7085   $124.71   $124.70   $124.70  
  Purchase #6 $15.94   11.616%   $17.7916   $17.79   $17.80   $17.80  
  Purchase #7 $157.84   5.555%   $166.608   $166.61   $166.60   $166.60  
  7 purchase totals = $795.84       $844.8592   $844.87   $844.85   $844.90