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 $248.50   13.287%   $281.5182   $281.52   $281.50   $281.50  
  Purchase #2 $226.50   11.430%   $252.389   $252.39   $252.40   $252.40  
  Purchase #3 $24.54   12.167%   $27.5258   $27.53   $27.55   $27.50  
  Purchase #4 $23.68   11.575%   $26.421   $26.42   $26.40   $26.40  
  Purchase #5 $229.43   8.853%   $249.7414   $249.74   $249.75   $249.70  
  Purchase #6 $175.27   6.364%   $186.4242   $186.42   $186.40   $186.40  
  Purchase #7 $30.55   10.475%   $33.7501   $33.75   $33.75   $33.80  
  7 purchase totals = $958.47       $1,057.7697   $1,057.77   $1,057.75   $1,057.70