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 $247.62   8.749%   $269.2843   $269.28   $269.30   $269.30  
  Purchase #2 $6.86   12.719%   $7.7325   $7.73   $7.75   $7.70  
  Purchase #3 $114.55   9.189%   $125.076   $125.08   $125.10   $125.10  
  Purchase #4 $60.91   7.117%   $65.245   $65.25   $65.25   $65.20  
  Purchase #5 $32.60   7.667%   $35.0994   $35.10   $35.10   $35.10  
  Purchase #6 $213.73   9.712%   $234.4875   $234.49   $234.50   $234.50  
  Purchase #7 $56.74   4.177%   $59.11   $59.11   $59.10   $59.10  
  7 purchase totals = $733.01       $796.0347   $796.04   $796.10   $796.00