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 $55.67   9.677%   $61.0572   $61.06   $61.05   $61.10  
  Purchase #2 $250.86   9.269%   $274.1122   $274.11   $274.10   $274.10  
  Purchase #3 $90.79   5.611%   $95.8842   $95.88   $95.90   $95.90  
  Purchase #4 $24.89   5.664%   $26.2998   $26.30   $26.30   $26.30  
  Purchase #5 $23.84   6.463%   $25.3808   $25.38   $25.40   $25.40  
  Purchase #6 $170.61   3.839%   $177.1597   $177.16   $177.15   $177.20  
  Purchase #7 $243.66   9.498%   $266.8028   $266.80   $266.80   $266.80  
  7 purchase totals = $860.32       $926.6967   $926.69   $926.70   $926.80