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 $36.63   12.165%   $41.086   $41.09   $41.10   $41.10  
  Purchase #2 $152.73   5.382%   $160.9499   $160.95   $160.95   $160.90  
  Purchase #3 $25.38   8.150%   $27.4485   $27.45   $27.45   $27.40  
  Purchase #4 $196.67   5.336%   $207.1643   $207.16   $207.15   $207.20  
  Purchase #5 $77.77   9.444%   $85.1146   $85.11   $85.10   $85.10  
  Purchase #6 $165.70   6.309%   $176.154   $176.15   $176.15   $176.20  
  Purchase #7 $89.36   8.825%   $97.246   $97.25   $97.25   $97.20  
  7 purchase totals = $744.24       $795.1633   $795.16   $795.15   $795.10