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 $179.53   13.647%   $204.0305   $204.03   $204.05   $204.00  
  Purchase #2 $237.72   6.136%   $252.3065   $252.31   $252.30   $252.30  
  Purchase #3 $83.28   9.158%   $90.9068   $90.91   $90.90   $90.90  
  Purchase #4 $237.36   6.214%   $252.1096   $252.11   $252.10   $252.10  
  Purchase #5 $217.89   10.574%   $240.9297   $240.93   $240.95   $240.90  
  Purchase #6 $55.75   11.208%   $61.9985   $62.00   $62.00   $62.00  
  Purchase #7 $153.26   3.267%   $158.267   $158.27   $158.25   $158.30  
  7 purchase totals = $1,164.79       $1,260.5486   $1,260.56   $1,260.55   $1,260.50