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 $51.81   9.246%   $56.6004   $56.60   $56.60   $56.60  
  Purchase #2 $237.94   3.867%   $247.1411   $247.14   $247.15   $247.10  
  Purchase #3 $72.53   11.508%   $80.8768   $80.88   $80.90   $80.90  
  Purchase #4 $60.94   12.299%   $68.435   $68.44   $68.45   $68.40  
  Purchase #5 $102.52   4.591%   $107.2267   $107.23   $107.25   $107.20  
  Purchase #6 $97.67   7.765%   $105.2541   $105.25   $105.25   $105.30  
  Purchase #7 $241.65   8.466%   $262.1081   $262.11   $262.10   $262.10  
  7 purchase totals = $865.06       $927.6422   $927.65   $927.70   $927.60