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 $105.73   12.568%   $119.0181   $119.02   $119.00   $119.00  
  Purchase #2 $11.62   10.563%   $12.8474   $12.85   $12.85   $12.80  
  Purchase #3 $44.99   7.123%   $48.1946   $48.19   $48.20   $48.20  
  Purchase #4 $247.50   5.587%   $261.3278   $261.33   $261.35   $261.30  
  Purchase #5 $8.34   10.789%   $9.2398   $9.24   $9.25   $9.20  
  Purchase #6 $67.82   8.699%   $73.7197   $73.72   $73.70   $73.70  
  Purchase #7 $162.71   9.860%   $178.7532   $178.75   $178.75   $178.80  
  7 purchase totals = $648.71       $703.1006   $703.10   $703.10   $703.00