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 $241.54   8.528%   $262.1385   $262.14   $262.15   $262.10  
  Purchase #2 $73.35   11.754%   $81.9716   $81.97   $81.95   $82.00  
  Purchase #3 $145.78   5.576%   $153.9087   $153.91   $153.90   $153.90  
  Purchase #4 $42.52   8.275%   $46.0385   $46.04   $46.05   $46.00  
  Purchase #5 $9.57   4.248%   $9.9765   $9.98   $10.00   $10.00  
  Purchase #6 $86.53   9.337%   $94.6093   $94.61   $94.60   $94.60  
  Purchase #7 $69.50   10.867%   $77.0526   $77.05   $77.05   $77.10  
  7 purchase totals = $668.79       $725.6957   $725.70   $725.70   $725.70