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 $106.38   6.155%   $112.9277   $112.93   $112.95   $112.90  
  Purchase #2 $111.66   10.359%   $123.2269   $123.23   $123.25   $123.20  
  Purchase #3 $164.41   6.235%   $174.661   $174.66   $174.65   $174.70  
  Purchase #4 $214.42   4.118%   $223.2498   $223.25   $223.25   $223.20  
  Purchase #5 $186.37   3.222%   $192.3748   $192.37   $192.35   $192.40  
  Purchase #6 $26.95   10.813%   $29.8641   $29.86   $29.85   $29.90  
  Purchase #7 $96.58   6.326%   $102.6897   $102.69   $102.70   $102.70  
  7 purchase totals = $906.77       $958.9940   $958.99   $959.00   $959.00