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 $226.49   11.558%   $252.6677   $252.67   $252.65   $252.70  
  Purchase #2 $247.52   5.537%   $261.2252   $261.23   $261.25   $261.20  
  Purchase #3 $215.33   8.689%   $234.04   $234.04   $234.05   $234.00  
  Purchase #4 $236.79   5.256%   $249.2357   $249.24   $249.25   $249.20  
  Purchase #5 $38.81   13.373%   $44.0001   $44.00   $44.00   $44.00  
  Purchase #6 $19.80   8.155%   $21.4147   $21.41   $21.40   $21.40  
  Purchase #7 $13.51   5.297%   $14.2256   $14.23   $14.25   $14.20  
  7 purchase totals = $998.25       $1,076.8090   $1,076.82   $1,076.85   $1,076.70