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 $204.64   6.644%   $218.2363   $218.24   $218.25   $218.20  
  Purchase #2 $60.58   7.395%   $65.0599   $65.06   $65.05   $65.10  
  Purchase #3 $39.62   6.249%   $42.0959   $42.10   $42.10   $42.10  
  Purchase #4 $139.32   12.554%   $156.8102   $156.81   $156.80   $156.80  
  Purchase #5 $176.73   6.153%   $187.6042   $187.60   $187.60   $187.60  
  Purchase #6 $25.79   8.296%   $27.9295   $27.93   $27.95   $27.90  
  Purchase #7 $53.41   5.518%   $56.3572   $56.36   $56.35   $56.40  
  7 purchase totals = $700.09       $754.0932   $754.10   $754.10   $754.10