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 $221.62   8.275%   $239.9591   $239.96   $239.95   $240.00  
  Purchase #2 $42.89   11.236%   $47.7091   $47.71   $47.70   $47.70  
  Purchase #3 $61.67   7.874%   $66.5259   $66.53   $66.55   $66.50  
  Purchase #4 $93.35   7.496%   $100.3475   $100.35   $100.35   $100.30  
  Purchase #5 $243.77   7.573%   $262.2307   $262.23   $262.25   $262.20  
  Purchase #6 $196.59   11.399%   $218.9993   $219.00   $219.00   $219.00  
  Purchase #7 $116.38   10.871%   $129.0317   $129.03   $129.05   $129.00  
  7 purchase totals = $976.27       $1,064.8033   $1,064.81   $1,064.85   $1,064.70