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 $162.41   4.692%   $170.0303   $170.03   $170.05   $170.00  
  Purchase #2 $84.83   9.426%   $92.8261   $92.83   $92.85   $92.80  
  Purchase #3 $220.85   11.487%   $246.219   $246.22   $246.20   $246.20  
  Purchase #4 $77.33   11.607%   $86.3057   $86.31   $86.30   $86.30  
  Purchase #5 $28.41   11.496%   $31.676   $31.68   $31.70   $31.70  
  Purchase #6 $122.80   9.533%   $134.5065   $134.51   $134.50   $134.50  
  Purchase #7 $57.30   6.544%   $61.0497   $61.05   $61.05   $61.00  
  7 purchase totals = $753.93       $822.6133   $822.63   $822.65   $822.50