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 $231.55   6.194%   $245.8922   $245.89   $245.90   $245.90  
  Purchase #2 $182.46   8.413%   $197.8104   $197.81   $197.80   $197.80  
  Purchase #3 $176.86   3.273%   $182.6486   $182.65   $182.65   $182.60  
  Purchase #4 $114.52   4.630%   $119.8223   $119.82   $119.80   $119.80  
  Purchase #5 $207.91   13.719%   $236.4332   $236.43   $236.45   $236.40  
  Purchase #6 $11.84   5.749%   $12.5207   $12.52   $12.50   $12.50  
  Purchase #7 $53.88   5.688%   $56.9447   $56.94   $56.95   $56.90  
  7 purchase totals = $979.02       $1,052.0721   $1,052.06   $1,052.05   $1,051.90