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 $218.32   13.736%   $248.3084   $248.31   $248.30   $248.30  
  Purchase #2 $24.54   11.281%   $27.3084   $27.31   $27.30   $27.30  
  Purchase #3 $80.53   3.286%   $83.1762   $83.18   $83.20   $83.20  
  Purchase #4 $113.49   10.172%   $125.0342   $125.03   $125.05   $125.00  
  Purchase #5 $139.56   6.713%   $148.9287   $148.93   $148.95   $148.90  
  Purchase #6 $201.31   3.646%   $208.6498   $208.65   $208.65   $208.60  
  Purchase #7 $209.99   6.261%   $223.1375   $223.14   $223.15   $223.10  
  7 purchase totals = $987.74       $1,064.5432   $1,064.55   $1,064.60   $1,064.40