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 $74.81   9.260%   $81.7374   $81.74   $81.75   $81.70  
  Purchase #2 $243.53   10.583%   $269.3028   $269.30   $269.30   $269.30  
  Purchase #3 $234.70   6.605%   $250.2019   $250.20   $250.20   $250.20  
  Purchase #4 $234.88   10.575%   $259.7186   $259.72   $259.70   $259.70  
  Purchase #5 $176.61   4.616%   $184.7623   $184.76   $184.75   $184.80  
  Purchase #6 $32.69   6.206%   $34.7187   $34.72   $34.70   $34.70  
  Purchase #7 $163.73   13.299%   $185.5045   $185.50   $185.50   $185.50  
  7 purchase totals = $1,160.95       $1,265.9462   $1,265.94   $1,265.90   $1,265.90