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 $246.88   9.330%   $269.9139   $269.91   $269.90   $269.90  
  Purchase #2 $150.51   8.552%   $163.3816   $163.38   $163.40   $163.40  
  Purchase #3 $121.31   13.521%   $137.7123   $137.71   $137.70   $137.70  
  Purchase #4 $186.80   8.382%   $202.4576   $202.46   $202.45   $202.50  
  Purchase #5 $229.33   12.202%   $257.3128   $257.31   $257.30   $257.30  
  Purchase #6 $69.30   3.659%   $71.8357   $71.84   $71.85   $71.80  
  Purchase #7 $60.92   8.596%   $66.1567   $66.16   $66.15   $66.20  
  7 purchase totals = $1,065.05       $1,168.7706   $1,168.77   $1,168.75   $1,168.80