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 $231.89   6.102%   $246.0399   $246.04   $246.05   $246.00  
  Purchase #2 $221.43   7.780%   $238.6573   $238.66   $238.65   $238.70  
  Purchase #3 $40.26   4.537%   $42.0866   $42.09   $42.10   $42.10  
  Purchase #4 $61.92   13.534%   $70.3003   $70.30   $70.30   $70.30  
  Purchase #5 $122.43   4.827%   $128.3397   $128.34   $128.35   $128.30  
  Purchase #6 $108.57   4.508%   $113.4643   $113.46   $113.45   $113.50  
  Purchase #7 $177.36   5.747%   $187.5529   $187.55   $187.55   $187.60  
  7 purchase totals = $963.86       $1,026.4410   $1,026.44   $1,026.45   $1,026.50