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 $61.79   5.690%   $65.3059   $65.31   $65.30   $65.30  
  Purchase #2 $95.60   3.320%   $98.7739   $98.77   $98.75   $98.80  
  Purchase #3 $248.80   8.549%   $270.0699   $270.07   $270.05   $270.10  
  Purchase #4 $41.37   11.738%   $46.226   $46.23   $46.25   $46.20  
  Purchase #5 $96.48   6.852%   $103.0908   $103.09   $103.10   $103.10  
  Purchase #6 $103.46   9.568%   $113.3591   $113.36   $113.35   $113.40  
  Purchase #7 $230.55   3.621%   $238.8982   $238.90   $238.90   $238.90  
  7 purchase totals = $878.05       $935.7238   $935.73   $935.70   $935.80