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 $68.91   9.368%   $75.3655   $75.37   $75.35   $75.40  
  Purchase #2 $171.29   11.828%   $191.5502   $191.55   $191.55   $191.60  
  Purchase #3 $148.46   12.225%   $166.6092   $166.61   $166.60   $166.60  
  Purchase #4 $122.75   11.744%   $137.1658   $137.17   $137.15   $137.20  
  Purchase #5 $66.54   4.212%   $69.3427   $69.34   $69.35   $69.30  
  Purchase #6 $208.62   4.438%   $217.8786   $217.88   $217.90   $217.90  
  Purchase #7 $129.81   4.686%   $135.8929   $135.89   $135.90   $135.90  
  7 purchase totals = $916.38       $993.8049   $993.81   $993.80   $993.90