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 $241.89   6.722%   $258.1498   $258.15   $258.15   $258.10  
  Purchase #2 $189.41   12.697%   $213.4594   $213.46   $213.45   $213.50  
  Purchase #3 $73.36   5.167%   $77.1505   $77.15   $77.15   $77.20  
  Purchase #4 $106.41   11.401%   $118.5418   $118.54   $118.55   $118.50  
  Purchase #5 $177.67   10.694%   $196.67   $196.67   $196.65   $196.70  
  Purchase #6 $65.88   11.805%   $73.6571   $73.66   $73.65   $73.70  
  Purchase #7 $188.47   7.601%   $202.7956   $202.80   $202.80   $202.80  
  7 purchase totals = $1,043.09       $1,140.4242   $1,140.43   $1,140.40   $1,140.50