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 $224.51   11.258%   $249.7853   $249.79   $249.80   $249.80  
  Purchase #2 $88.81   10.532%   $98.1635   $98.16   $98.15   $98.20  
  Purchase #3 $90.41   6.306%   $96.1113   $96.11   $96.10   $96.10  
  Purchase #4 $177.44   7.253%   $190.3097   $190.31   $190.30   $190.30  
  Purchase #5 $70.28   8.553%   $76.291   $76.29   $76.30   $76.30  
  Purchase #6 $152.96   12.328%   $171.8169   $171.82   $171.80   $171.80  
  Purchase #7 $69.25   12.130%   $77.65   $77.65   $77.65   $77.70  
  7 purchase totals = $873.66       $960.1277   $960.13   $960.10   $960.20