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 $164.57   8.358%   $178.3248   $178.32   $178.30   $178.30  
  Purchase #2 $15.25   6.659%   $16.2655   $16.27   $16.25   $16.30  
  Purchase #3 $150.41   7.535%   $161.7434   $161.74   $161.75   $161.70  
  Purchase #4 $241.61   5.801%   $255.6258   $255.63   $255.65   $255.60  
  Purchase #5 $184.32   8.616%   $200.201   $200.20   $200.20   $200.20  
  Purchase #6 $239.83   13.326%   $271.7897   $271.79   $271.80   $271.80  
  Purchase #7 $79.27   3.664%   $82.1745   $82.17   $82.15   $82.20  
  7 purchase totals = $1,075.26       $1,166.1247   $1,166.12   $1,166.10   $1,166.10