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 $62.53   5.423%   $65.921   $65.92   $65.90   $65.90  
  Purchase #2 $98.44   8.668%   $106.9728   $106.97   $106.95   $107.00  
  Purchase #3 $238.52   13.776%   $271.3785   $271.38   $271.40   $271.40  
  Purchase #4 $124.68   12.827%   $140.6727   $140.67   $140.65   $140.70  
  Purchase #5 $223.37   12.263%   $250.7619   $250.76   $250.75   $250.80  
  Purchase #6 $218.45   9.863%   $239.9957   $240.00   $240.00   $240.00  
  Purchase #7 $197.63   11.689%   $220.731   $220.73   $220.75   $220.70  
  7 purchase totals = $1,163.62       $1,296.4336   $1,296.43   $1,296.40   $1,296.50