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 $205.81   7.528%   $221.3034   $221.30   $221.30   $221.30  
  Purchase #2 $203.67   12.761%   $229.6603   $229.66   $229.65   $229.70  
  Purchase #3 $15.54   13.743%   $17.6757   $17.68   $17.70   $17.70  
  Purchase #4 $227.29   11.482%   $253.3874   $253.39   $253.40   $253.40  
  Purchase #5 $228.99   10.624%   $253.3179   $253.32   $253.30   $253.30  
  Purchase #6 $208.66   13.233%   $236.272   $236.27   $236.25   $236.30  
  Purchase #7 $158.88   3.735%   $164.8142   $164.81   $164.80   $164.80  
  7 purchase totals = $1,248.84       $1,376.4309   $1,376.43   $1,376.40   $1,376.50