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 $54.86   10.235%   $60.4749   $60.47   $60.45   $60.50  
  Purchase #2 $179.36   13.511%   $203.5933   $203.59   $203.60   $203.60  
  Purchase #3 $34.79   4.444%   $36.3361   $36.34   $36.35   $36.30  
  Purchase #4 $134.86   3.223%   $139.2065   $139.21   $139.20   $139.20  
  Purchase #5 $225.27   12.174%   $252.6944   $252.69   $252.70   $252.70  
  Purchase #6 $157.41   13.489%   $178.643   $178.64   $178.65   $178.60  
  Purchase #7 $168.31   7.345%   $180.6724   $180.67   $180.65   $180.70  
  7 purchase totals = $954.86       $1,051.6206   $1,051.61   $1,051.60   $1,051.60