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 $65.35   11.745%   $73.0254   $73.03   $73.05   $73.00  
  Purchase #2 $220.74   11.141%   $245.3326   $245.33   $245.35   $245.30  
  Purchase #3 $223.95   12.723%   $252.4432   $252.44   $252.45   $252.40  
  Purchase #4 $139.43   10.275%   $153.7564   $153.76   $153.75   $153.80  
  Purchase #5 $229.70   3.641%   $238.0634   $238.06   $238.05   $238.10  
  Purchase #6 $62.37   9.501%   $68.2958   $68.30   $68.30   $68.30  
  Purchase #7 $221.83   8.186%   $239.989   $239.99   $240.00   $240.00  
  7 purchase totals = $1,163.37       $1,270.9058   $1,270.91   $1,270.95   $1,270.90