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 $204.62   13.857%   $232.9742   $232.97   $232.95   $233.00  
  Purchase #2 $215.36   12.242%   $241.7244   $241.72   $241.70   $241.70  
  Purchase #3 $178.39   3.404%   $184.4624   $184.46   $184.45   $184.50  
  Purchase #4 $13.26   6.244%   $14.088   $14.09   $14.10   $14.10  
  Purchase #5 $179.89   12.542%   $202.4518   $202.45   $202.45   $202.50  
  Purchase #6 $229.91   8.119%   $248.5764   $248.58   $248.60   $248.60  
  Purchase #7 $122.44   13.299%   $138.7233   $138.72   $138.70   $138.70  
  7 purchase totals = $1,143.87       $1,263.0005   $1,262.99   $1,262.95   $1,263.10