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 $229.48   6.724%   $244.9102   $244.91   $244.90   $244.90  
  Purchase #2 $130.55   4.134%   $135.9469   $135.95   $135.95   $135.90  
  Purchase #3 $24.82   7.770%   $26.7485   $26.75   $26.75   $26.70  
  Purchase #4 $106.97   3.762%   $110.9942   $110.99   $111.00   $111.00  
  Purchase #5 $101.39   11.661%   $113.2131   $113.21   $113.20   $113.20  
  Purchase #6 $191.69   11.249%   $213.2532   $213.25   $213.25   $213.30  
  Purchase #7 $59.45   3.781%   $61.6978   $61.70   $61.70   $61.70  
  7 purchase totals = $844.35       $906.7639   $906.76   $906.75   $906.70