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 $44.69   11.764%   $49.9473   $49.95   $49.95   $49.90  
  Purchase #2 $41.45   11.873%   $46.3714   $46.37   $46.35   $46.40  
  Purchase #3 $121.37   5.567%   $128.1267   $128.13   $128.15   $128.10  
  Purchase #4 $109.86   11.740%   $122.7576   $122.76   $122.75   $122.80  
  Purchase #5 $55.96   10.677%   $61.9348   $61.93   $61.95   $61.90  
  Purchase #6 $87.92   11.650%   $98.1627   $98.16   $98.15   $98.20  
  Purchase #7 $193.94   13.228%   $219.5944   $219.59   $219.60   $219.60  
  7 purchase totals = $655.19       $726.8949   $726.89   $726.90   $726.90