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 $243.75   7.160%   $261.2025   $261.20   $261.20   $261.20  
  Purchase #2 $201.42   4.456%   $210.3953   $210.40   $210.40   $210.40  
  Purchase #3 $55.27   6.182%   $58.6868   $58.69   $58.70   $58.70  
  Purchase #4 $161.92   11.530%   $180.5894   $180.59   $180.60   $180.60  
  Purchase #5 $232.41   9.291%   $254.0032   $254.00   $254.00   $254.00  
  Purchase #6 $177.97   10.150%   $196.034   $196.03   $196.05   $196.00  
  Purchase #7 $223.71   11.511%   $249.4613   $249.46   $249.45   $249.50  
  7 purchase totals = $1,296.45       $1,410.3725   $1,410.37   $1,410.40   $1,410.40