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 $201.45   11.366%   $224.3468   $224.35   $224.35   $224.30  
  Purchase #2 $245.62   13.299%   $278.285   $278.29   $278.30   $278.30  
  Purchase #3 $159.74   11.274%   $177.7491   $177.75   $177.75   $177.70  
  Purchase #4 $32.31   9.242%   $35.2961   $35.30   $35.30   $35.30  
  Purchase #5 $231.36   6.358%   $246.0699   $246.07   $246.05   $246.10  
  Purchase #6 $13.83   5.587%   $14.6027   $14.60   $14.60   $14.60  
  Purchase #7 $168.88   11.467%   $188.2455   $188.25   $188.25   $188.20  
  7 purchase totals = $1,053.19       $1,164.5951   $1,164.61   $1,164.60   $1,164.50