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 $29.57   11.869%   $33.0797   $33.08   $33.10   $33.10  
  Purchase #2 $173.39   13.584%   $196.9433   $196.94   $196.95   $196.90  
  Purchase #3 $207.41   10.404%   $228.9889   $228.99   $229.00   $229.00  
  Purchase #4 $216.92   8.397%   $235.1348   $235.13   $235.15   $235.10  
  Purchase #5 $222.93   4.299%   $232.5138   $232.51   $232.50   $232.50  
  Purchase #6 $63.76   8.681%   $69.295   $69.30   $69.30   $69.30  
  Purchase #7 $26.27   6.513%   $27.981   $27.98   $28.00   $28.00  
  7 purchase totals = $940.25       $1,023.9365   $1,023.93   $1,024.00   $1,023.90