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 $209.89   3.842%   $217.954   $217.95   $217.95   $218.00  
  Purchase #2 $145.61   7.225%   $156.1303   $156.13   $156.15   $156.10  
  Purchase #3 $115.42   11.238%   $128.3909   $128.39   $128.40   $128.40  
  Purchase #4 $250.53   4.552%   $261.9341   $261.93   $261.95   $261.90  
  Purchase #5 $106.78   12.172%   $119.7773   $119.78   $119.80   $119.80  
  Purchase #6 $202.73   12.353%   $227.7732   $227.77   $227.75   $227.80  
  Purchase #7 $134.95   11.445%   $150.395   $150.40   $150.40   $150.40  
  7 purchase totals = $1,165.91       $1,262.3548   $1,262.35   $1,262.40   $1,262.40