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 $193.40   10.236%   $213.1964   $213.20   $213.20   $213.20  
  Purchase #2 $234.52   12.361%   $263.509   $263.51   $263.50   $263.50  
  Purchase #3 $224.62   3.318%   $232.0729   $232.07   $232.05   $232.10  
  Purchase #4 $218.30   13.778%   $248.3774   $248.38   $248.40   $248.40  
  Purchase #5 $35.61   4.690%   $37.2801   $37.28   $37.30   $37.30  
  Purchase #6 $71.44   8.142%   $77.2566   $77.26   $77.25   $77.30  
  Purchase #7 $131.43   10.167%   $144.7925   $144.79   $144.80   $144.80  
  7 purchase totals = $1,109.32       $1,216.4849   $1,216.49   $1,216.50   $1,216.60