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 $16.96   12.399%   $19.0629   $19.06   $19.05   $19.10  
  Purchase #2 $226.48   6.645%   $241.5296   $241.53   $241.55   $241.50  
  Purchase #3 $101.91   12.140%   $114.2819   $114.28   $114.30   $114.30  
  Purchase #4 $166.96   9.253%   $182.4088   $182.41   $182.40   $182.40  
  Purchase #5 $85.49   12.139%   $95.8676   $95.87   $95.85   $95.90  
  Purchase #6 $107.77   5.702%   $113.915   $113.92   $113.90   $113.90  
  Purchase #7 $244.92   8.484%   $265.699   $265.70   $265.70   $265.70  
  7 purchase totals = $950.49       $1,032.7648   $1,032.77   $1,032.75   $1,032.80