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 $58.67   5.728%   $62.0306   $62.03   $62.05   $62.00  
  Purchase #2 $46.31   11.239%   $51.5148   $51.51   $51.50   $51.50  
  Purchase #3 $154.27   13.293%   $174.7771   $174.78   $174.80   $174.80  
  Purchase #4 $117.83   3.222%   $121.6265   $121.63   $121.65   $121.60  
  Purchase #5 $122.87   11.307%   $136.7629   $136.76   $136.75   $136.80  
  Purchase #6 $47.61   8.298%   $51.5607   $51.56   $51.55   $51.60  
  Purchase #7 $101.39   9.255%   $110.7736   $110.77   $110.75   $110.80  
  7 purchase totals = $648.95       $709.0462   $709.04   $709.05   $709.10