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 $165.25   8.560%   $179.3954   $179.40   $179.40   $179.40  
  Purchase #2 $136.45   11.359%   $151.9494   $151.95   $151.95   $151.90  
  Purchase #3 $168.57   7.619%   $181.4133   $181.41   $181.40   $181.40  
  Purchase #4 $126.50   6.664%   $134.93   $134.93   $134.95   $134.90  
  Purchase #5 $11.78   13.658%   $13.3889   $13.39   $13.40   $13.40  
  Purchase #6 $228.93   12.285%   $257.0541   $257.05   $257.05   $257.10  
  Purchase #7 $116.72   8.543%   $126.6914   $126.69   $126.70   $126.70  
  7 purchase totals = $954.20       $1,044.8225   $1,044.82   $1,044.85   $1,044.80