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 $246.62   5.332%   $259.7698   $259.77   $259.75   $259.80  
  Purchase #2 $183.44   6.433%   $195.2407   $195.24   $195.25   $195.20  
  Purchase #3 $39.47   7.102%   $42.2732   $42.27   $42.25   $42.30  
  Purchase #4 $165.46   12.254%   $185.7355   $185.74   $185.75   $185.70  
  Purchase #5 $111.61   13.552%   $126.7354   $126.74   $126.75   $126.70  
  Purchase #6 $116.50   7.809%   $125.5975   $125.60   $125.60   $125.60  
  Purchase #7 $190.76   4.359%   $199.0752   $199.08   $199.10   $199.10  
  7 purchase totals = $1,053.86       $1,134.4273   $1,134.44   $1,134.45   $1,134.40