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 $60.60   4.526%   $63.3428   $63.34   $63.35   $63.30  
  Purchase #2 $247.38   9.289%   $270.3591   $270.36   $270.35   $270.40  
  Purchase #3 $89.35   10.722%   $98.9301   $98.93   $98.95   $98.90  
  Purchase #4 $97.70   9.677%   $107.1544   $107.15   $107.15   $107.20  
  Purchase #5 $82.84   4.627%   $86.673   $86.67   $86.65   $86.70  
  Purchase #6 $153.91   9.564%   $168.63   $168.63   $168.65   $168.60  
  Purchase #7 $163.91   12.363%   $184.1742   $184.17   $184.15   $184.20  
  7 purchase totals = $895.69       $979.2636   $979.25   $979.25   $979.30