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 $26.55   9.561%   $29.0884   $29.09   $29.10   $29.10  
  Purchase #2 $113.50   7.394%   $121.8922   $121.89   $121.90   $121.90  
  Purchase #3 $42.62   12.256%   $47.8435   $47.84   $47.85   $47.80  
  Purchase #4 $82.36   6.620%   $87.8122   $87.81   $87.80   $87.80  
  Purchase #5 $148.47   11.724%   $165.8766   $165.88   $165.90   $165.90  
  Purchase #6 $62.65   10.555%   $69.2627   $69.26   $69.25   $69.30  
  Purchase #7 $16.42   9.368%   $17.9582   $17.96   $17.95   $18.00  
  7 purchase totals = $492.57       $539.7338   $539.73   $539.75   $539.80