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 $157.88   11.788%   $176.4909   $176.49   $176.50   $176.50  
  Purchase #2 $76.83   12.422%   $86.3738   $86.37   $86.35   $86.40  
  Purchase #3 $154.84   13.423%   $175.6242   $175.62   $175.60   $175.60  
  Purchase #4 $83.70   5.193%   $88.0465   $88.05   $88.05   $88.00  
  Purchase #5 $86.72   7.468%   $93.1962   $93.20   $93.20   $93.20  
  Purchase #6 $187.62   8.561%   $203.6821   $203.68   $203.70   $203.70  
  Purchase #7 $167.91   11.474%   $187.176   $187.18   $187.20   $187.20  
  7 purchase totals = $915.50       $1,010.5897   $1,010.59   $1,010.60   $1,010.60