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 $98.93   5.723%   $104.5918   $104.59   $104.60   $104.60  
  Purchase #2 $200.79   8.108%   $217.0701   $217.07   $217.05   $217.10  
  Purchase #3 $61.74   7.703%   $66.4958   $66.50   $66.50   $66.50  
  Purchase #4 $216.77   4.819%   $227.2161   $227.22   $227.20   $227.20  
  Purchase #5 $169.87   11.125%   $188.768   $188.77   $188.75   $188.80  
  Purchase #6 $151.53   6.275%   $161.0385   $161.04   $161.05   $161.00  
  Purchase #7 $217.30   10.554%   $240.2338   $240.23   $240.25   $240.20  
  7 purchase totals = $1,116.93       $1,205.4141   $1,205.42   $1,205.40   $1,205.40