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 $208.56   11.233%   $231.9875   $231.99   $232.00   $232.00  
  Purchase #2 $115.30   3.578%   $119.4254   $119.43   $119.45   $119.40  
  Purchase #3 $177.99   13.238%   $201.5523   $201.55   $201.55   $201.60  
  Purchase #4 $95.40   4.630%   $99.817   $99.82   $99.80   $99.80  
  Purchase #5 $134.82   7.219%   $144.5527   $144.55   $144.55   $144.60  
  Purchase #6 $8.58   11.646%   $9.5792   $9.58   $9.60   $9.60  
  Purchase #7 $16.46   6.138%   $17.4703   $17.47   $17.45   $17.50  
  7 purchase totals = $757.11       $824.3844   $824.39   $824.40   $824.50