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 $51.61   5.486%   $54.4413   $54.44   $54.45   $54.40  
  Purchase #2 $233.61   8.153%   $252.6562   $252.66   $252.65   $252.70  
  Purchase #3 $235.64   7.828%   $254.0859   $254.09   $254.10   $254.10  
  Purchase #4 $61.77   12.815%   $69.6858   $69.69   $69.70   $69.70  
  Purchase #5 $183.42   6.608%   $195.5404   $195.54   $195.55   $195.50  
  Purchase #6 $147.29   6.164%   $156.369   $156.37   $156.35   $156.40  
  Purchase #7 $51.31   12.774%   $57.8643   $57.86   $57.85   $57.90  
  7 purchase totals = $964.65       $1,040.6429   $1,040.65   $1,040.65   $1,040.70