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 $83.32   11.768%   $93.1251   $93.13   $93.15   $93.10  
  Purchase #2 $241.92   8.392%   $262.2219   $262.22   $262.20   $262.20  
  Purchase #3 $50.68   13.371%   $57.4564   $57.46   $57.45   $57.50  
  Purchase #4 $204.63   10.476%   $226.067   $226.07   $226.05   $226.10  
  Purchase #5 $37.72   9.125%   $41.162   $41.16   $41.15   $41.20  
  Purchase #6 $107.69   6.476%   $114.664   $114.66   $114.65   $114.70  
  Purchase #7 $224.71   12.751%   $253.3628   $253.36   $253.35   $253.40  
  7 purchase totals = $950.67       $1,048.0592   $1,048.06   $1,048.00   $1,048.20