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 $248.70   10.140%   $273.9182   $273.92   $273.90   $273.90  
  Purchase #2 $209.99   7.321%   $225.3634   $225.36   $225.35   $225.40  
  Purchase #3 $14.50   10.694%   $16.0506   $16.05   $16.05   $16.10  
  Purchase #4 $144.61   3.117%   $149.1175   $149.12   $149.10   $149.10  
  Purchase #5 $133.44   5.222%   $140.4082   $140.41   $140.40   $140.40  
  Purchase #6 $34.32   10.712%   $37.9964   $38.00   $38.00   $38.00  
  Purchase #7 $200.35   3.372%   $207.1058   $207.11   $207.10   $207.10  
  7 purchase totals = $985.91       $1,049.9601   $1,049.97   $1,049.90   $1,050.00