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 $88.66   5.131%   $93.2091   $93.21   $93.20   $93.20  
  Purchase #2 $49.85   7.864%   $53.7702   $53.77   $53.75   $53.80  
  Purchase #3 $145.60   4.120%   $151.5987   $151.60   $151.60   $151.60  
  Purchase #4 $72.38   3.344%   $74.8004   $74.80   $74.80   $74.80  
  Purchase #5 $51.82   8.523%   $56.2366   $56.24   $56.25   $56.20  
  Purchase #6 $212.50   12.592%   $239.258   $239.26   $239.25   $239.30  
  Purchase #7 $46.64   4.340%   $48.6642   $48.66   $48.65   $48.70  
  7 purchase totals = $667.45       $717.5372   $717.54   $717.50   $717.60