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 $55.92   4.822%   $58.6165   $58.62   $58.60   $58.60  
  Purchase #2 $208.48   10.798%   $230.9917   $230.99   $231.00   $231.00  
  Purchase #3 $245.61   6.828%   $262.3803   $262.38   $262.40   $262.40  
  Purchase #4 $50.95   12.717%   $57.4293   $57.43   $57.45   $57.40  
  Purchase #5 $107.41   11.343%   $119.5935   $119.59   $119.60   $119.60  
  Purchase #6 $20.36   3.190%   $21.0095   $21.01   $21.00   $21.00  
  Purchase #7 $63.92   12.453%   $71.88   $71.88   $71.90   $71.90  
  7 purchase totals = $752.65       $821.9008   $821.90   $821.95   $821.90