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 $57.92   11.479%   $64.5686   $64.57   $64.55   $64.60  
  Purchase #2 $47.89   8.116%   $51.7768   $51.78   $51.80   $51.80  
  Purchase #3 $128.94   3.856%   $133.9119   $133.91   $133.90   $133.90  
  Purchase #4 $228.61   7.396%   $245.518   $245.52   $245.50   $245.50  
  Purchase #5 $227.55   5.309%   $239.6306   $239.63   $239.65   $239.60  
  Purchase #6 $163.32   11.486%   $182.0789   $182.08   $182.10   $182.10  
  Purchase #7 $171.53   8.740%   $186.5217   $186.52   $186.50   $186.50  
  7 purchase totals = $1,025.76       $1,104.0065   $1,104.01   $1,104.00   $1,104.00