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 $202.90   7.422%   $217.9592   $217.96   $217.95   $218.00  
  Purchase #2 $146.29   3.483%   $151.3853   $151.39   $151.40   $151.40  
  Purchase #3 $164.43   11.631%   $183.5549   $183.55   $183.55   $183.60  
  Purchase #4 $179.42   11.820%   $200.6274   $200.63   $200.65   $200.60  
  Purchase #5 $148.51   3.498%   $153.7049   $153.70   $153.70   $153.70  
  Purchase #6 $89.98   7.804%   $97.002   $97.00   $97.00   $97.00  
  Purchase #7 $232.95   12.461%   $261.9779   $261.98   $262.00   $262.00  
  7 purchase totals = $1,164.48       $1,266.2116   $1,266.21   $1,266.25   $1,266.30