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 $241.82   11.445%   $269.4963   $269.50   $269.50   $269.50  
  Purchase #2 $220.88   12.384%   $248.2338   $248.23   $248.25   $248.20  
  Purchase #3 $226.65   7.162%   $242.8827   $242.88   $242.90   $242.90  
  Purchase #4 $236.83   5.441%   $249.7159   $249.72   $249.70   $249.70  
  Purchase #5 $177.76   13.514%   $201.7825   $201.78   $201.80   $201.80  
  Purchase #6 $27.94   3.563%   $28.9355   $28.94   $28.95   $28.90  
  Purchase #7 $193.94   4.841%   $203.3286   $203.33   $203.35   $203.30  
  7 purchase totals = $1,325.82       $1,444.3753   $1,444.38   $1,444.45   $1,444.30