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 $55.51   8.502%   $60.2295   $60.23   $60.25   $60.20  
  Purchase #2 $120.53   13.826%   $137.1945   $137.19   $137.20   $137.20  
  Purchase #3 $174.98   4.158%   $182.2557   $182.26   $182.25   $182.30  
  Purchase #4 $196.81   10.475%   $217.4258   $217.43   $217.45   $217.40  
  Purchase #5 $208.95   13.569%   $237.3024   $237.30   $237.30   $237.30  
  Purchase #6 $163.87   10.486%   $181.0534   $181.05   $181.05   $181.10  
  Purchase #7 $18.59   13.832%   $21.1614   $21.16   $21.15   $21.20  
  7 purchase totals = $939.24       $1,036.6227   $1,036.62   $1,036.65   $1,036.70