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 $222.49   11.718%   $248.5614   $248.56   $248.55   $248.60  
  Purchase #2 $226.65   6.839%   $242.1506   $242.15   $242.15   $242.20  
  Purchase #3 $82.97   13.620%   $94.2705   $94.27   $94.25   $94.30  
  Purchase #4 $154.91   6.291%   $164.6554   $164.66   $164.65   $164.70  
  Purchase #5 $197.63   6.337%   $210.1538   $210.15   $210.15   $210.20  
  Purchase #6 $226.73   7.566%   $243.8844   $243.88   $243.90   $243.90  
  Purchase #7 $182.70   4.533%   $190.9818   $190.98   $191.00   $191.00  
  7 purchase totals = $1,294.08       $1,394.6579   $1,394.65   $1,394.65   $1,394.90