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 $239.73   12.601%   $269.9384   $269.94   $269.95   $269.90  
  Purchase #2 $196.39   3.794%   $203.841   $203.84   $203.85   $203.80  
  Purchase #3 $35.84   6.856%   $38.2972   $38.30   $38.30   $38.30  
  Purchase #4 $60.80   3.171%   $62.728   $62.73   $62.75   $62.70  
  Purchase #5 $192.77   11.815%   $215.5458   $215.55   $215.55   $215.50  
  Purchase #6 $193.92   6.664%   $206.8428   $206.84   $206.85   $206.80  
  Purchase #7 $230.43   9.411%   $252.1158   $252.12   $252.10   $252.10  
  7 purchase totals = $1,149.88       $1,249.3090   $1,249.32   $1,249.35   $1,249.10