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 $196.76   5.202%   $206.9955   $207.00   $207.00   $207.00  
  Purchase #2 $194.84   11.238%   $216.7361   $216.74   $216.75   $216.70  
  Purchase #3 $185.46   9.284%   $202.6781   $202.68   $202.70   $202.70  
  Purchase #4 $50.40   9.664%   $55.2707   $55.27   $55.25   $55.30  
  Purchase #5 $101.94   13.786%   $115.9934   $115.99   $116.00   $116.00  
  Purchase #6 $185.94   6.746%   $198.4835   $198.48   $198.50   $198.50  
  Purchase #7 $223.61   12.764%   $252.1516   $252.15   $252.15   $252.20  
  7 purchase totals = $1,138.95       $1,248.3089   $1,248.31   $1,248.35   $1,248.40