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 $36.28   6.411%   $38.6059   $38.61   $38.60   $38.60  
  Purchase #2 $103.87   9.421%   $113.6556   $113.66   $113.65   $113.70  
  Purchase #3 $79.30   8.584%   $86.1071   $86.11   $86.10   $86.10  
  Purchase #4 $240.40   11.321%   $267.6157   $267.62   $267.60   $267.60  
  Purchase #5 $130.30   6.759%   $139.107   $139.11   $139.10   $139.10  
  Purchase #6 $135.69   13.211%   $153.616   $153.62   $153.60   $153.60  
  Purchase #7 $5.38   10.439%   $5.9416   $5.94   $5.95   $5.90  
  7 purchase totals = $731.22       $804.6489   $804.67   $804.60   $804.60