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 $201.84   6.327%   $214.6104   $214.61   $214.60   $214.60  
  Purchase #2 $244.81   13.239%   $277.2204   $277.22   $277.20   $277.20  
  Purchase #3 $30.57   3.870%   $31.7531   $31.75   $31.75   $31.80  
  Purchase #4 $47.57   12.669%   $53.5966   $53.60   $53.60   $53.60  
  Purchase #5 $113.52   8.677%   $123.3701   $123.37   $123.35   $123.40  
  Purchase #6 $23.60   5.529%   $24.9048   $24.90   $24.90   $24.90  
  Purchase #7 $233.75   5.786%   $247.2748   $247.27   $247.25   $247.30  
  7 purchase totals = $895.66       $972.7302   $972.72   $972.65   $972.80