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 $72.98   8.551%   $79.2205   $79.22   $79.20   $79.20  
  Purchase #2 $159.48   12.672%   $179.6893   $179.69   $179.70   $179.70  
  Purchase #3 $106.27   12.525%   $119.5803   $119.58   $119.60   $119.60  
  Purchase #4 $13.56   7.633%   $14.595   $14.60   $14.60   $14.60  
  Purchase #5 $237.46   4.512%   $248.1742   $248.17   $248.15   $248.20  
  Purchase #6 $98.90   10.203%   $108.9908   $108.99   $109.00   $109.00  
  Purchase #7 $10.51   8.811%   $11.436   $11.44   $11.45   $11.40  
  7 purchase totals = $699.16       $761.6861   $761.69   $761.70   $761.70