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 $96.49   3.783%   $100.1402   $100.14   $100.15   $100.10  
  Purchase #2 $224.64   5.259%   $236.4538   $236.45   $236.45   $236.50  
  Purchase #3 $189.73   6.784%   $202.6013   $202.60   $202.60   $202.60  
  Purchase #4 $81.98   3.599%   $84.9305   $84.93   $84.95   $84.90  
  Purchase #5 $170.41   13.609%   $193.6011   $193.60   $193.60   $193.60  
  Purchase #6 $116.89   6.314%   $124.2704   $124.27   $124.25   $124.30  
  Purchase #7 $118.35   12.726%   $133.4112   $133.41   $133.40   $133.40  
  7 purchase totals = $998.49       $1,075.4085   $1,075.40   $1,075.40   $1,075.40