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 $227.88   3.371%   $235.5618   $235.56   $235.55   $235.60  
  Purchase #2 $194.93   11.685%   $217.7076   $217.71   $217.70   $217.70  
  Purchase #3 $132.25   8.795%   $143.8814   $143.88   $143.90   $143.90  
  Purchase #4 $183.64   7.158%   $196.785   $196.79   $196.80   $196.80  
  Purchase #5 $86.38   6.469%   $91.9679   $91.97   $91.95   $92.00  
  Purchase #6 $246.47   3.427%   $254.9165   $254.92   $254.90   $254.90  
  Purchase #7 $190.76   11.839%   $213.3441   $213.34   $213.35   $213.30  
  7 purchase totals = $1,262.31       $1,354.1643   $1,354.17   $1,354.15   $1,354.20