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 $115.51   9.147%   $126.0757   $126.08   $126.10   $126.10  
  Purchase #2 $168.35   10.432%   $185.9123   $185.91   $185.90   $185.90  
  Purchase #3 $244.54   6.188%   $259.6721   $259.67   $259.65   $259.70  
  Purchase #4 $81.82   5.470%   $86.2956   $86.30   $86.30   $86.30  
  Purchase #5 $145.47   6.801%   $155.3634   $155.36   $155.35   $155.40  
  Purchase #6 $152.30   6.789%   $162.6396   $162.64   $162.65   $162.60  
  Purchase #7 $208.60   10.707%   $230.9348   $230.93   $230.95   $230.90  
  7 purchase totals = $1,116.59       $1,206.8935   $1,206.89   $1,206.90   $1,206.90