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 $56.36   12.795%   $63.5713   $63.57   $63.55   $63.60  
  Purchase #2 $250.38   12.200%   $280.9264   $280.93   $280.95   $280.90  
  Purchase #3 $62.79   6.831%   $67.0792   $67.08   $67.10   $67.10  
  Purchase #4 $6.65   6.628%   $7.0908   $7.09   $7.10   $7.10  
  Purchase #5 $224.46   10.732%   $248.549   $248.55   $248.55   $248.50  
  Purchase #6 $123.78   12.449%   $139.1894   $139.19   $139.20   $139.20  
  Purchase #7 $201.69   12.831%   $227.5688   $227.57   $227.55   $227.60  
  7 purchase totals = $926.11       $1,033.9749   $1,033.98   $1,034.00   $1,034.00