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 $115.71   8.485%   $125.528   $125.53   $125.55   $125.50  
  Purchase #2 $148.45   8.286%   $160.7506   $160.75   $160.75   $160.80  
  Purchase #3 $34.97   12.629%   $39.3864   $39.39   $39.40   $39.40  
  Purchase #4 $157.78   5.379%   $166.267   $166.27   $166.25   $166.30  
  Purchase #5 $152.66   5.865%   $161.6135   $161.61   $161.60   $161.60  
  Purchase #6 $54.41   3.526%   $56.3285   $56.33   $56.35   $56.30  
  Purchase #7 $24.55   8.447%   $26.6237   $26.62   $26.60   $26.60  
  7 purchase totals = $688.53       $736.4977   $736.50   $736.50   $736.50