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 $53.66   7.345%   $57.6013   $57.60   $57.60   $57.60  
  Purchase #2 $208.44   6.560%   $222.1137   $222.11   $222.10   $222.10  
  Purchase #3 $213.50   6.188%   $226.7114   $226.71   $226.70   $226.70  
  Purchase #4 $152.51   10.598%   $168.673   $168.67   $168.65   $168.70  
  Purchase #5 $24.74   5.699%   $26.1499   $26.15   $26.15   $26.10  
  Purchase #6 $132.63   12.223%   $148.8414   $148.84   $148.85   $148.80  
  Purchase #7 $156.33   11.640%   $174.5268   $174.53   $174.55   $174.50  
  7 purchase totals = $941.81       $1,024.6175   $1,024.61   $1,024.60   $1,024.50