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 $68.57   11.735%   $76.6167   $76.62   $76.60   $76.60  
  Purchase #2 $125.28   11.391%   $139.5506   $139.55   $139.55   $139.60  
  Purchase #3 $26.46   6.685%   $28.2289   $28.23   $28.25   $28.20  
  Purchase #4 $141.66   7.308%   $152.0125   $152.01   $152.00   $152.00  
  Purchase #5 $197.84   3.188%   $204.1471   $204.15   $204.15   $204.10  
  Purchase #6 $46.72   6.219%   $49.6255   $49.63   $49.65   $49.60  
  Purchase #7 $163.84   5.853%   $173.4296   $173.43   $173.45   $173.40  
  7 purchase totals = $770.37       $823.6109   $823.62   $823.65   $823.50