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 $53.88   8.455%   $58.4356   $58.44   $58.45   $58.40  
  Purchase #2 $58.84   13.340%   $66.6893   $66.69   $66.70   $66.70  
  Purchase #3 $152.98   8.442%   $165.8946   $165.89   $165.90   $165.90  
  Purchase #4 $105.47   8.114%   $114.0278   $114.03   $114.05   $114.00  
  Purchase #5 $75.89   11.662%   $84.7403   $84.74   $84.75   $84.70  
  Purchase #6 $106.66   9.260%   $116.5367   $116.54   $116.55   $116.50  
  Purchase #7 $92.68   6.333%   $98.5494   $98.55   $98.55   $98.50  
  7 purchase totals = $646.40       $704.8737   $704.88   $704.95   $704.70