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 $7.61   3.600%   $7.884   $7.88   $7.90   $7.90  
  Purchase #2 $198.59   10.223%   $218.8919   $218.89   $218.90   $218.90  
  Purchase #3 $184.41   4.837%   $193.3299   $193.33   $193.35   $193.30  
  Purchase #4 $240.95   10.622%   $266.5437   $266.54   $266.55   $266.50  
  Purchase #5 $119.71   9.185%   $130.7054   $130.71   $130.70   $130.70  
  Purchase #6 $99.68   9.753%   $109.4018   $109.40   $109.40   $109.40  
  Purchase #7 $175.70   9.537%   $192.4565   $192.46   $192.45   $192.50  
  7 purchase totals = $1,026.65       $1,119.2132   $1,119.21   $1,119.25   $1,119.20