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 $190.76   8.395%   $206.7743   $206.77   $206.75   $206.80  
  Purchase #2 $210.78   13.808%   $239.8845   $239.88   $239.90   $239.90  
  Purchase #3 $154.68   13.574%   $175.6763   $175.68   $175.70   $175.70  
  Purchase #4 $131.39   13.597%   $149.2551   $149.26   $149.25   $149.30  
  Purchase #5 $81.83   12.471%   $92.035   $92.04   $92.05   $92.00  
  Purchase #6 $165.67   8.657%   $180.0121   $180.01   $180.00   $180.00  
  Purchase #7 $14.72   4.495%   $15.3817   $15.38   $15.40   $15.40  
  7 purchase totals = $949.83       $1,059.0190   $1,059.02   $1,059.05   $1,059.10