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 $49.63   13.180%   $56.1712   $56.17   $56.15   $56.20  
  Purchase #2 $115.37   6.602%   $122.9867   $122.99   $123.00   $123.00  
  Purchase #3 $14.93   7.744%   $16.0862   $16.09   $16.10   $16.10  
  Purchase #4 $241.44   11.246%   $268.5923   $268.59   $268.60   $268.60  
  Purchase #5 $199.90   9.324%   $218.5387   $218.54   $218.55   $218.50  
  Purchase #6 $187.64   9.182%   $204.8691   $204.87   $204.85   $204.90  
  Purchase #7 $97.77   10.150%   $107.6937   $107.69   $107.70   $107.70  
  7 purchase totals = $906.68       $994.9379   $994.94   $994.95   $995.00