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 $32.62   6.796%   $34.8369   $34.84   $34.85   $34.80  
  Purchase #2 $158.88   7.393%   $170.626   $170.63   $170.65   $170.60  
  Purchase #3 $40.46   13.664%   $45.9885   $45.99   $46.00   $46.00  
  Purchase #4 $249.55   7.215%   $267.555   $267.56   $267.55   $267.60  
  Purchase #5 $32.97   7.558%   $35.4619   $35.46   $35.45   $35.50  
  Purchase #6 $154.46   12.750%   $174.1537   $174.15   $174.15   $174.20  
  Purchase #7 $67.78   6.474%   $72.1681   $72.17   $72.15   $72.20  
  7 purchase totals = $736.72       $800.7901   $800.80   $800.80   $800.90