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 $62.48   4.283%   $65.156   $65.16   $65.15   $65.20  
  Purchase #2 $49.84   4.109%   $51.8879   $51.89   $51.90   $51.90  
  Purchase #3 $72.75   12.457%   $81.8125   $81.81   $81.80   $81.80  
  Purchase #4 $144.36   13.584%   $163.9699   $163.97   $163.95   $164.00  
  Purchase #5 $237.44   12.866%   $267.989   $267.99   $268.00   $268.00  
  Purchase #6 $95.86   7.489%   $103.039   $103.04   $103.05   $103.00  
  Purchase #7 $37.87   8.859%   $41.2249   $41.22   $41.20   $41.20  
  7 purchase totals = $700.60       $775.0792   $775.08   $775.05   $775.10