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 $86.42   12.653%   $97.3547   $97.35   $97.35   $97.40  
  Purchase #2 $123.67   8.132%   $133.7268   $133.73   $133.75   $133.70  
  Purchase #3 $145.98   12.495%   $164.2202   $164.22   $164.20   $164.20  
  Purchase #4 $172.88   3.681%   $179.2437   $179.24   $179.25   $179.20  
  Purchase #5 $84.73   13.759%   $96.388   $96.39   $96.40   $96.40  
  Purchase #6 $249.82   10.481%   $276.0036   $276.00   $276.00   $276.00  
  Purchase #7 $175.72   4.801%   $184.1563   $184.16   $184.15   $184.20  
  7 purchase totals = $1,039.22       $1,131.0933   $1,131.09   $1,131.10   $1,131.10