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 $247.69   5.641%   $261.6622   $261.66   $261.65   $261.70  
  Purchase #2 $66.96   13.140%   $75.7585   $75.76   $75.75   $75.80  
  Purchase #3 $178.53   13.176%   $202.0531   $202.05   $202.05   $202.10  
  Purchase #4 $67.28   5.319%   $70.8586   $70.86   $70.85   $70.90  
  Purchase #5 $157.34   10.564%   $173.9614   $173.96   $173.95   $174.00  
  Purchase #6 $51.38   6.487%   $54.713   $54.71   $54.70   $54.70  
  Purchase #7 $147.72   9.436%   $161.6589   $161.66   $161.65   $161.70  
  7 purchase totals = $916.90       $1,000.6657   $1,000.66   $1,000.60   $1,000.90