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 $55.54   6.658%   $59.2379   $59.24   $59.25   $59.20  
  Purchase #2 $68.74   10.652%   $76.0622   $76.06   $76.05   $76.10  
  Purchase #3 $31.50   3.309%   $32.5423   $32.54   $32.55   $32.50  
  Purchase #4 $127.36   8.536%   $138.2314   $138.23   $138.25   $138.20  
  Purchase #5 $14.73   12.454%   $16.5645   $16.56   $16.55   $16.60  
  Purchase #6 $201.84   9.557%   $221.1298   $221.13   $221.15   $221.10  
  Purchase #7 $56.66   11.182%   $62.9957   $63.00   $63.00   $63.00  
  7 purchase totals = $556.37       $606.7638   $606.76   $606.80   $606.70