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 $38.79   6.814%   $41.4332   $41.43   $41.45   $41.40  
  Purchase #2 $164.99   8.493%   $179.0026   $179.00   $179.00   $179.00  
  Purchase #3 $50.35   9.311%   $55.0381   $55.04   $55.05   $55.00  
  Purchase #4 $132.49   4.767%   $138.8058   $138.81   $138.80   $138.80  
  Purchase #5 $112.61   9.730%   $123.567   $123.57   $123.55   $123.60  
  Purchase #6 $248.56   7.266%   $266.6204   $266.62   $266.60   $266.60  
  Purchase #7 $249.69   3.717%   $258.971   $258.97   $258.95   $259.00  
  7 purchase totals = $997.48       $1,063.4381   $1,063.44   $1,063.40   $1,063.40