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 $22.79   10.509%   $25.185   $25.19   $25.20   $25.20  
  Purchase #2 $68.46   12.288%   $76.8724   $76.87   $76.85   $76.90  
  Purchase #3 $223.34   5.258%   $235.0832   $235.08   $235.10   $235.10  
  Purchase #4 $23.38   8.182%   $25.293   $25.29   $25.30   $25.30  
  Purchase #5 $158.32   9.398%   $173.1989   $173.20   $173.20   $173.20  
  Purchase #6 $55.83   8.459%   $60.5527   $60.55   $60.55   $60.60  
  Purchase #7 $166.44   6.784%   $177.7313   $177.73   $177.75   $177.70  
  7 purchase totals = $718.56       $773.9165   $773.91   $773.95   $774.00