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 $30.60   9.526%   $33.515   $33.52   $33.50   $33.50  
  Purchase #2 $14.59   11.445%   $16.2598   $16.26   $16.25   $16.30  
  Purchase #3 $62.95   11.662%   $70.2912   $70.29   $70.30   $70.30  
  Purchase #4 $41.90   13.752%   $47.6621   $47.66   $47.65   $47.70  
  Purchase #5 $95.93   6.389%   $102.059   $102.06   $102.05   $102.10  
  Purchase #6 $103.27   9.480%   $113.06   $113.06   $113.05   $113.10  
  Purchase #7 $170.41   3.524%   $176.4152   $176.42   $176.40   $176.40  
  7 purchase totals = $519.65       $559.2623   $559.27   $559.20   $559.40