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 $51.92   11.388%   $57.8326   $57.83   $57.85   $57.80  
  Purchase #2 $57.83   10.184%   $63.7194   $63.72   $63.70   $63.70  
  Purchase #3 $201.29   3.330%   $207.993   $207.99   $208.00   $208.00  
  Purchase #4 $87.39   13.252%   $98.9709   $98.97   $98.95   $99.00  
  Purchase #5 $58.27   10.502%   $64.3895   $64.39   $64.40   $64.40  
  Purchase #6 $209.37   5.208%   $220.274   $220.27   $220.25   $220.30  
  Purchase #7 $232.50   12.683%   $261.988   $261.99   $262.00   $262.00  
  7 purchase totals = $898.57       $975.1674   $975.16   $975.15   $975.20