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 $53.57   13.151%   $60.615   $60.62   $60.60   $60.60  
  Purchase #2 $45.26   11.682%   $50.5473   $50.55   $50.55   $50.50  
  Purchase #3 $51.57   10.657%   $57.0658   $57.07   $57.05   $57.10  
  Purchase #4 $168.64   8.503%   $182.9795   $182.98   $183.00   $183.00  
  Purchase #5 $41.59   10.202%   $45.833   $45.83   $45.85   $45.80  
  Purchase #6 $239.46   7.333%   $257.0196   $257.02   $257.00   $257.00  
  Purchase #7 $41.81   7.838%   $45.0871   $45.09   $45.10   $45.10  
  7 purchase totals = $641.90       $699.1473   $699.16   $699.15   $699.10