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 $56.94   6.420%   $60.5955   $60.60   $60.60   $60.60  
  Purchase #2 $33.59   12.517%   $37.7945   $37.79   $37.80   $37.80  
  Purchase #3 $8.25   5.616%   $8.7133   $8.71   $8.70   $8.70  
  Purchase #4 $248.46   6.737%   $265.1988   $265.20   $265.20   $265.20  
  Purchase #5 $197.77   9.151%   $215.8679   $215.87   $215.85   $215.90  
  Purchase #6 $183.41   12.673%   $206.6535   $206.65   $206.65   $206.70  
  Purchase #7 $141.66   10.498%   $156.5315   $156.53   $156.55   $156.50  
  7 purchase totals = $870.08       $951.3550   $951.35   $951.35   $951.40