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 $178.27   12.739%   $200.9798   $200.98   $201.00   $201.00  
  Purchase #2 $75.92   13.223%   $85.9589   $85.96   $85.95   $86.00  
  Purchase #3 $73.63   12.373%   $82.7402   $82.74   $82.75   $82.70  
  Purchase #4 $235.59   10.279%   $259.8063   $259.81   $259.80   $259.80  
  Purchase #5 $248.60   11.723%   $277.7434   $277.74   $277.75   $277.70  
  Purchase #6 $116.75   10.542%   $129.0578   $129.06   $129.05   $129.10  
  Purchase #7 $57.53   10.856%   $63.7755   $63.78   $63.80   $63.80  
  7 purchase totals = $986.29       $1,100.0619   $1,100.07   $1,100.10   $1,100.10