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 $186.43   6.606%   $198.7456   $198.75   $198.75   $198.70  
  Purchase #2 $248.38   8.574%   $269.6761   $269.68   $269.70   $269.70  
  Purchase #3 $62.32   12.486%   $70.1013   $70.10   $70.10   $70.10  
  Purchase #4 $241.78   12.247%   $271.3908   $271.39   $271.40   $271.40  
  Purchase #5 $133.88   3.310%   $138.3114   $138.31   $138.30   $138.30  
  Purchase #6 $206.75   3.394%   $213.7671   $213.77   $213.75   $213.80  
  Purchase #7 $43.69   6.705%   $46.6194   $46.62   $46.60   $46.60  
  7 purchase totals = $1,123.23       $1,208.6117   $1,208.62   $1,208.60   $1,208.60