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 $205.54   4.744%   $215.2908   $215.29   $215.30   $215.30  
  Purchase #2 $131.29   12.543%   $147.7577   $147.76   $147.75   $147.80  
  Purchase #3 $48.77   6.258%   $51.822   $51.82   $51.80   $51.80  
  Purchase #4 $188.45   8.854%   $205.1354   $205.14   $205.15   $205.10  
  Purchase #5 $60.51   10.801%   $67.0457   $67.05   $67.05   $67.00  
  Purchase #6 $63.68   7.434%   $68.414   $68.41   $68.40   $68.40  
  Purchase #7 $237.99   13.691%   $270.5732   $270.57   $270.55   $270.60  
  7 purchase totals = $936.23       $1,026.0388   $1,026.04   $1,026.00   $1,026.00