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 $228.74   5.382%   $241.0508   $241.05   $241.05   $241.10  
  Purchase #2 $194.78   9.319%   $212.9315   $212.93   $212.95   $212.90  
  Purchase #3 $122.99   10.676%   $136.1204   $136.12   $136.10   $136.10  
  Purchase #4 $156.65   9.368%   $171.325   $171.33   $171.35   $171.30  
  Purchase #5 $240.66   8.822%   $261.891   $261.89   $261.90   $261.90  
  Purchase #6 $190.44   6.792%   $203.3747   $203.37   $203.35   $203.40  
  Purchase #7 $90.37   11.657%   $100.9044   $100.90   $100.90   $100.90  
  7 purchase totals = $1,224.63       $1,327.5978   $1,327.59   $1,327.60   $1,327.60