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 $104.71   8.170%   $113.2648   $113.26   $113.25   $113.30  
  Purchase #2 $72.70   10.743%   $80.5102   $80.51   $80.50   $80.50  
  Purchase #3 $130.56   9.784%   $143.334   $143.33   $143.35   $143.30  
  Purchase #4 $24.52   9.193%   $26.7741   $26.77   $26.75   $26.80  
  Purchase #5 $237.87   3.170%   $245.4105   $245.41   $245.40   $245.40  
  Purchase #6 $231.68   11.698%   $258.7819   $258.78   $258.80   $258.80  
  Purchase #7 $163.73   10.758%   $181.3441   $181.34   $181.35   $181.30  
  7 purchase totals = $965.77       $1,049.4196   $1,049.40   $1,049.40   $1,049.40