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 $54.47   5.232%   $57.3199   $57.32   $57.30   $57.30  
  Purchase #2 $208.44   13.342%   $236.2501   $236.25   $236.25   $236.30  
  Purchase #3 $78.60   5.389%   $82.8358   $82.84   $82.85   $82.80  
  Purchase #4 $109.95   8.712%   $119.5288   $119.53   $119.55   $119.50  
  Purchase #5 $74.26   12.610%   $83.6242   $83.62   $83.60   $83.60  
  Purchase #6 $196.55   13.860%   $223.7918   $223.79   $223.80   $223.80  
  Purchase #7 $84.81   11.623%   $94.6675   $94.67   $94.65   $94.70  
  7 purchase totals = $807.08       $898.0181   $898.02   $898.00   $898.00