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 $248.26   8.604%   $269.6203   $269.62   $269.60   $269.60  
  Purchase #2 $157.77   8.517%   $171.2073   $171.21   $171.20   $171.20  
  Purchase #3 $110.88   4.516%   $115.8873   $115.89   $115.90   $115.90  
  Purchase #4 $32.53   12.113%   $36.4704   $36.47   $36.45   $36.50  
  Purchase #5 $162.70   3.138%   $167.8055   $167.81   $167.80   $167.80  
  Purchase #6 $218.62   13.429%   $247.9785   $247.98   $248.00   $248.00  
  Purchase #7 $163.43   7.124%   $175.0728   $175.07   $175.05   $175.10  
  7 purchase totals = $1,094.19       $1,184.0421   $1,184.05   $1,184.00   $1,184.10