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 $56.58   7.784%   $60.9842   $60.98   $61.00   $61.00  
  Purchase #2 $62.46   11.247%   $69.4849   $69.48   $69.50   $69.50  
  Purchase #3 $81.55   7.155%   $87.3849   $87.38   $87.40   $87.40  
  Purchase #4 $109.44   11.457%   $121.9785   $121.98   $122.00   $122.00  
  Purchase #5 $107.91   6.296%   $114.704   $114.70   $114.70   $114.70  
  Purchase #6 $213.92   8.521%   $232.1481   $232.15   $232.15   $232.10  
  Purchase #7 $193.91   3.722%   $201.1273   $201.13   $201.15   $201.10  
  7 purchase totals = $825.77       $887.8119   $887.80   $887.90   $887.80