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 $217.65   9.798%   $238.9753   $238.98   $239.00   $239.00  
  Purchase #2 $139.93   9.281%   $152.9169   $152.92   $152.90   $152.90  
  Purchase #3 $33.64   4.147%   $35.0351   $35.04   $35.05   $35.00  
  Purchase #4 $219.36   7.760%   $236.3823   $236.38   $236.40   $236.40  
  Purchase #5 $225.52   6.855%   $240.9794   $240.98   $241.00   $241.00  
  Purchase #6 $187.83   5.681%   $198.5006   $198.50   $198.50   $198.50  
  Purchase #7 $225.69   12.719%   $254.3955   $254.40   $254.40   $254.40  
  7 purchase totals = $1,249.62       $1,357.1851   $1,357.20   $1,357.25   $1,357.20