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 $114.94   12.341%   $129.1247   $129.12   $129.10   $129.10  
  Purchase #2 $195.32   4.798%   $204.6915   $204.69   $204.70   $204.70  
  Purchase #3 $56.31   9.615%   $61.7242   $61.72   $61.70   $61.70  
  Purchase #4 $208.42   13.271%   $236.0794   $236.08   $236.10   $236.10  
  Purchase #5 $239.81   4.228%   $249.9492   $249.95   $249.95   $249.90  
  Purchase #6 $108.32   12.584%   $121.951   $121.95   $121.95   $122.00  
  Purchase #7 $13.99   5.706%   $14.7883   $14.79   $14.80   $14.80  
  7 purchase totals = $937.11       $1,018.3083   $1,018.30   $1,018.30   $1,018.30