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 $55.93   11.704%   $62.476   $62.48   $62.50   $62.50  
  Purchase #2 $25.46   12.380%   $28.6119   $28.61   $28.60   $28.60  
  Purchase #3 $155.38   5.189%   $163.4427   $163.44   $163.45   $163.40  
  Purchase #4 $91.72   9.441%   $100.3793   $100.38   $100.40   $100.40  
  Purchase #5 $194.28   10.144%   $213.9878   $213.99   $214.00   $214.00  
  Purchase #6 $250.84   12.578%   $282.3907   $282.39   $282.40   $282.40  
  Purchase #7 $135.90   6.606%   $144.8776   $144.88   $144.90   $144.90  
  7 purchase totals = $909.51       $996.1660   $996.17   $996.25   $996.20