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 $54.97   13.658%   $62.4778   $62.48   $62.50   $62.50  
  Purchase #2 $226.46   9.786%   $248.6214   $248.62   $248.60   $248.60  
  Purchase #3 $6.59   7.147%   $7.061   $7.06   $7.05   $7.10  
  Purchase #4 $239.75   4.256%   $249.9538   $249.95   $249.95   $250.00  
  Purchase #5 $48.91   6.651%   $52.163   $52.16   $52.15   $52.20  
  Purchase #6 $168.86   6.830%   $180.3931   $180.39   $180.40   $180.40  
  Purchase #7 $63.54   7.200%   $68.1149   $68.11   $68.10   $68.10  
  7 purchase totals = $809.08       $868.7850   $868.77   $868.75   $868.90