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 $235.38   13.837%   $267.9495   $267.95   $267.95   $267.90  
  Purchase #2 $115.38   8.314%   $124.9727   $124.97   $124.95   $125.00  
  Purchase #3 $217.75   7.365%   $233.7873   $233.79   $233.80   $233.80  
  Purchase #4 $159.69   5.653%   $168.7173   $168.72   $168.70   $168.70  
  Purchase #5 $65.88   11.186%   $73.2493   $73.25   $73.25   $73.20  
  Purchase #6 $84.34   5.462%   $88.9467   $88.95   $88.95   $88.90  
  Purchase #7 $122.97   6.524%   $130.9926   $130.99   $131.00   $131.00  
  7 purchase totals = $1,001.39       $1,088.6154   $1,088.62   $1,088.60   $1,088.50