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 $202.25   3.251%   $208.8251   $208.83   $208.85   $208.80  
  Purchase #2 $94.36   10.804%   $104.5547   $104.55   $104.55   $104.60  
  Purchase #3 $152.61   11.183%   $169.6764   $169.68   $169.70   $169.70  
  Purchase #4 $214.73   6.688%   $229.0911   $229.09   $229.10   $229.10  
  Purchase #5 $46.86   10.365%   $51.717   $51.72   $51.70   $51.70  
  Purchase #6 $174.66   8.530%   $189.5585   $189.56   $189.55   $189.60  
  Purchase #7 $231.40   3.313%   $239.0663   $239.07   $239.05   $239.10  
  7 purchase totals = $1,116.87       $1,192.4891   $1,192.50   $1,192.50   $1,192.60