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 $202.53   12.863%   $228.5814   $228.58   $228.60   $228.60  
  Purchase #2 $45.96   9.794%   $50.4613   $50.46   $50.45   $50.50  
  Purchase #3 $156.29   6.579%   $166.5723   $166.57   $166.55   $166.60  
  Purchase #4 $208.86   6.814%   $223.0917   $223.09   $223.10   $223.10  
  Purchase #5 $201.82   12.116%   $226.2725   $226.27   $226.25   $226.30  
  Purchase #6 $122.35   13.238%   $138.5467   $138.55   $138.55   $138.50  
  Purchase #7 $248.70   5.296%   $261.8712   $261.87   $261.85   $261.90  
  7 purchase totals = $1,186.51       $1,295.3971   $1,295.39   $1,295.35   $1,295.50