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 $220.60   8.632%   $239.6422   $239.64   $239.65   $239.60  
  Purchase #2 $93.31   10.571%   $103.1738   $103.17   $103.15   $103.20  
  Purchase #3 $106.62   6.708%   $113.7721   $113.77   $113.75   $113.80  
  Purchase #4 $178.69   10.829%   $198.0403   $198.04   $198.05   $198.00  
  Purchase #5 $225.64   10.512%   $249.3593   $249.36   $249.35   $249.40  
  Purchase #6 $230.46   7.784%   $248.399   $248.40   $248.40   $248.40  
  Purchase #7 $179.34   12.702%   $202.1198   $202.12   $202.10   $202.10  
  7 purchase totals = $1,234.66       $1,354.5065   $1,354.50   $1,354.45   $1,354.50