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 $226.76   11.497%   $252.8306   $252.83   $252.85   $252.80  
  Purchase #2 $135.66   9.814%   $148.9737   $148.97   $148.95   $149.00  
  Purchase #3 $88.36   6.448%   $94.0575   $94.06   $94.05   $94.10  
  Purchase #4 $247.39   5.391%   $260.7268   $260.73   $260.75   $260.70  
  Purchase #5 $126.69   10.455%   $139.9354   $139.94   $139.95   $139.90  
  Purchase #6 $62.25   3.755%   $64.5875   $64.59   $64.60   $64.60  
  Purchase #7 $65.52   3.459%   $67.7863   $67.79   $67.80   $67.80  
  7 purchase totals = $952.63       $1,028.8978   $1,028.91   $1,028.95   $1,028.90