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 $169.61   8.269%   $183.6351   $183.64   $183.65   $183.60  
  Purchase #2 $218.36   7.329%   $234.3636   $234.36   $234.35   $234.40  
  Purchase #3 $107.25   11.429%   $119.5076   $119.51   $119.50   $119.50  
  Purchase #4 $182.71   11.235%   $203.2375   $203.24   $203.25   $203.20  
  Purchase #5 $25.89   12.720%   $29.1832   $29.18   $29.20   $29.20  
  Purchase #6 $18.70   10.408%   $20.6463   $20.65   $20.65   $20.60  
  Purchase #7 $174.45   11.259%   $194.0913   $194.09   $194.10   $194.10  
  7 purchase totals = $896.97       $984.6646   $984.67   $984.70   $984.60