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 $96.63   11.466%   $107.7096   $107.71   $107.70   $107.70  
  Purchase #2 $108.85   5.177%   $114.4852   $114.49   $114.50   $114.50  
  Purchase #3 $35.45   5.536%   $37.4125   $37.41   $37.40   $37.40  
  Purchase #4 $240.30   6.259%   $255.3404   $255.34   $255.35   $255.30  
  Purchase #5 $22.43   7.852%   $24.1912   $24.19   $24.20   $24.20  
  Purchase #6 $150.98   8.812%   $164.2844   $164.28   $164.30   $164.30  
  Purchase #7 $122.54   6.464%   $130.461   $130.46   $130.45   $130.50  
  7 purchase totals = $777.18       $833.8843   $833.88   $833.90   $833.90