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 $52.62   12.321%   $59.1033   $59.10   $59.10   $59.10  
  Purchase #2 $236.83   7.396%   $254.3459   $254.35   $254.35   $254.30  
  Purchase #3 $205.81   6.412%   $219.0065   $219.01   $219.00   $219.00  
  Purchase #4 $69.56   7.605%   $74.85   $74.85   $74.85   $74.90  
  Purchase #5 $249.36   10.563%   $275.6999   $275.70   $275.70   $275.70  
  Purchase #6 $217.75   8.694%   $236.6812   $236.68   $236.70   $236.70  
  Purchase #7 $196.53   5.684%   $207.7008   $207.70   $207.70   $207.70  
  7 purchase totals = $1,228.46       $1,327.3876   $1,327.39   $1,327.40   $1,327.40