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 $54.73   12.564%   $61.6063   $61.61   $61.60   $61.60  
  Purchase #2 $241.79   3.213%   $249.5587   $249.56   $249.55   $249.60  
  Purchase #3 $147.36   7.366%   $158.2145   $158.21   $158.20   $158.20  
  Purchase #4 $85.89   13.476%   $97.4645   $97.46   $97.45   $97.50  
  Purchase #5 $218.92   13.421%   $248.3013   $248.30   $248.30   $248.30  
  Purchase #6 $49.87   13.671%   $56.6877   $56.69   $56.70   $56.70  
  Purchase #7 $21.87   4.477%   $22.8491   $22.85   $22.85   $22.80  
  7 purchase totals = $820.43       $894.6821   $894.68   $894.65   $894.70