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 $99.67   12.388%   $112.0171   $112.02   $112.00   $112.00  
  Purchase #2 $227.40   13.455%   $257.9967   $258.00   $258.00   $258.00  
  Purchase #3 $242.45   5.308%   $255.3192   $255.32   $255.30   $255.30  
  Purchase #4 $60.39   4.770%   $63.2706   $63.27   $63.25   $63.30  
  Purchase #5 $250.81   11.149%   $278.7728   $278.77   $278.75   $278.80  
  Purchase #6 $93.92   4.806%   $98.4338   $98.43   $98.45   $98.40  
  Purchase #7 $243.97   3.586%   $252.7188   $252.72   $252.70   $252.70  
  7 purchase totals = $1,218.61       $1,318.5290   $1,318.53   $1,318.45   $1,318.50