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 $241.33   7.161%   $258.6116   $258.61   $258.60   $258.60  
  Purchase #2 $249.97   13.812%   $284.4959   $284.50   $284.50   $284.50  
  Purchase #3 $39.94   8.192%   $43.2119   $43.21   $43.20   $43.20  
  Purchase #4 $207.74   13.812%   $236.433   $236.43   $236.45   $236.40  
  Purchase #5 $243.61   3.458%   $252.034   $252.03   $252.05   $252.00  
  Purchase #6 $147.81   12.723%   $166.6159   $166.62   $166.60   $166.60  
  Purchase #7 $239.36   3.331%   $247.3331   $247.33   $247.35   $247.30  
  7 purchase totals = $1,369.76       $1,488.7354   $1,488.73   $1,488.75   $1,488.60