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 $24.81   10.277%   $27.3597   $27.36   $27.35   $27.40  
  Purchase #2 $114.97   6.837%   $122.8305   $122.83   $122.85   $122.80  
  Purchase #3 $218.85   5.871%   $231.6987   $231.70   $231.70   $231.70  
  Purchase #4 $243.43   7.858%   $262.5587   $262.56   $262.55   $262.60  
  Purchase #5 $140.98   8.213%   $152.5587   $152.56   $152.55   $152.60  
  Purchase #6 $173.32   8.447%   $187.9603   $187.96   $187.95   $188.00  
  Purchase #7 $80.32   8.598%   $87.2259   $87.23   $87.25   $87.20  
  7 purchase totals = $996.68       $1,072.1925   $1,072.20   $1,072.20   $1,072.30