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 $207.83   13.811%   $236.5334   $236.53   $236.55   $236.50  
  Purchase #2 $116.90   12.440%   $131.4424   $131.44   $131.45   $131.40  
  Purchase #3 $15.67   13.757%   $17.8257   $17.83   $17.85   $17.80  
  Purchase #4 $247.80   4.272%   $258.386   $258.39   $258.40   $258.40  
  Purchase #5 $146.90   11.499%   $163.792   $163.79   $163.80   $163.80  
  Purchase #6 $185.78   10.659%   $205.5823   $205.58   $205.60   $205.60  
  Purchase #7 $236.50   6.150%   $251.0448   $251.04   $251.05   $251.00  
  7 purchase totals = $1,157.38       $1,264.6066   $1,264.60   $1,264.70   $1,264.50