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 $55.71   3.285%   $57.5401   $57.54   $57.55   $57.50  
  Purchase #2 $155.87   7.793%   $168.0169   $168.02   $168.00   $168.00  
  Purchase #3 $192.72   8.145%   $208.417   $208.42   $208.40   $208.40  
  Purchase #4 $24.46   11.365%   $27.2399   $27.24   $27.25   $27.20  
  Purchase #5 $234.71   9.826%   $257.7726   $257.77   $257.75   $257.80  
  Purchase #6 $156.37   3.417%   $161.7132   $161.71   $161.70   $161.70  
  Purchase #7 $68.62   8.608%   $74.5268   $74.53   $74.55   $74.50  
  7 purchase totals = $888.46       $955.2265   $955.23   $955.20   $955.10