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 $50.64   11.259%   $56.3416   $56.34   $56.35   $56.30  
  Purchase #2 $233.44   13.536%   $265.0384   $265.04   $265.05   $265.00  
  Purchase #3 $178.77   3.639%   $185.2754   $185.28   $185.30   $185.30  
  Purchase #4 $174.55   13.218%   $197.622   $197.62   $197.60   $197.60  
  Purchase #5 $144.80   5.385%   $152.5975   $152.60   $152.60   $152.60  
  Purchase #6 $161.98   4.130%   $168.6698   $168.67   $168.65   $168.70  
  Purchase #7 $180.37   11.143%   $200.4686   $200.47   $200.45   $200.50  
  7 purchase totals = $1,124.55       $1,226.0133   $1,226.02   $1,226.00   $1,226.00