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 $48.73   3.497%   $50.4341   $50.43   $50.45   $50.40  
  Purchase #2 $164.99   10.272%   $181.9378   $181.94   $181.95   $181.90  
  Purchase #3 $215.93   6.726%   $230.4535   $230.45   $230.45   $230.50  
  Purchase #4 $178.69   11.145%   $198.605   $198.61   $198.60   $198.60  
  Purchase #5 $109.58   12.832%   $123.6413   $123.64   $123.65   $123.60  
  Purchase #6 $229.32   5.199%   $241.2423   $241.24   $241.25   $241.20  
  Purchase #7 $184.56   8.722%   $200.6573   $200.66   $200.65   $200.70  
  7 purchase totals = $1,131.80       $1,226.9713   $1,226.97   $1,227.00   $1,226.90