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 $48.38   11.559%   $53.9722   $53.97   $53.95   $54.00  
  Purchase #2 $71.73   13.294%   $81.2658   $81.27   $81.25   $81.30  
  Purchase #3 $187.51   10.230%   $206.6923   $206.69   $206.70   $206.70  
  Purchase #4 $127.91   10.435%   $141.2574   $141.26   $141.25   $141.30  
  Purchase #5 $101.93   11.357%   $113.5062   $113.51   $113.50   $113.50  
  Purchase #6 $189.70   9.821%   $208.3304   $208.33   $208.35   $208.30  
  Purchase #7 $242.83   7.240%   $260.4109   $260.41   $260.40   $260.40  
  7 purchase totals = $969.99       $1,065.4352   $1,065.44   $1,065.40   $1,065.50