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 $147.99   11.829%   $165.4957   $165.50   $165.50   $165.50  
  Purchase #2 $44.58   4.316%   $46.5041   $46.50   $46.50   $46.50  
  Purchase #3 $215.63   3.627%   $223.4509   $223.45   $223.45   $223.50  
  Purchase #4 $190.51   11.328%   $212.091   $212.09   $212.10   $212.10  
  Purchase #5 $175.93   10.680%   $194.7193   $194.72   $194.70   $194.70  
  Purchase #6 $135.39   6.864%   $144.6832   $144.68   $144.70   $144.70  
  Purchase #7 $34.25   5.787%   $36.232   $36.23   $36.25   $36.20  
  7 purchase totals = $944.28       $1,023.1762   $1,023.17   $1,023.20   $1,023.20