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 $224.85   12.779%   $253.5836   $253.58   $253.60   $253.60  
  Purchase #2 $67.25   8.451%   $72.9333   $72.93   $72.95   $72.90  
  Purchase #3 $103.70   12.571%   $116.7361   $116.74   $116.75   $116.70  
  Purchase #4 $247.74   10.516%   $273.7923   $273.79   $273.80   $273.80  
  Purchase #5 $242.90   8.552%   $263.6728   $263.67   $263.65   $263.70  
  Purchase #6 $16.36   12.690%   $18.4361   $18.44   $18.45   $18.40  
  Purchase #7 $61.81   12.763%   $69.6988   $69.70   $69.70   $69.70  
  7 purchase totals = $964.61       $1,068.8530   $1,068.85   $1,068.90   $1,068.80