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 $180.81   13.336%   $204.9228   $204.92   $204.90   $204.90  
  Purchase #2 $58.87   8.413%   $63.8227   $63.82   $63.80   $63.80  
  Purchase #3 $59.25   7.799%   $63.8709   $63.87   $63.85   $63.90  
  Purchase #4 $115.54   9.540%   $126.5625   $126.56   $126.55   $126.60  
  Purchase #5 $222.51   8.476%   $241.3699   $241.37   $241.35   $241.40  
  Purchase #6 $246.41   11.810%   $275.511   $275.51   $275.50   $275.50  
  Purchase #7 $76.25   4.694%   $79.8292   $79.83   $79.85   $79.80  
  7 purchase totals = $959.64       $1,055.8890   $1,055.88   $1,055.80   $1,055.90