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 $52.77   13.806%   $60.0554   $60.06   $60.05   $60.10  
  Purchase #2 $80.45   8.154%   $87.0099   $87.01   $87.00   $87.00  
  Purchase #3 $226.86   3.680%   $235.2084   $235.21   $235.20   $235.20  
  Purchase #4 $53.38   5.663%   $56.4029   $56.40   $56.40   $56.40  
  Purchase #5 $55.70   6.833%   $59.506   $59.51   $59.50   $59.50  
  Purchase #6 $49.59   7.518%   $53.3182   $53.32   $53.30   $53.30  
  Purchase #7 $19.26   6.210%   $20.456   $20.46   $20.45   $20.50  
  7 purchase totals = $538.01       $571.9568   $571.97   $571.90   $572.00