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 $248.83   7.139%   $266.594   $266.59   $266.60   $266.60  
  Purchase #2 $157.54   5.119%   $165.6045   $165.60   $165.60   $165.60  
  Purchase #3 $179.51   12.717%   $202.3383   $202.34   $202.35   $202.30  
  Purchase #4 $235.37   11.689%   $262.8824   $262.88   $262.90   $262.90  
  Purchase #5 $41.40   13.396%   $46.9459   $46.95   $46.95   $46.90  
  Purchase #6 $157.89   10.213%   $174.0153   $174.02   $174.00   $174.00  
  Purchase #7 $43.62   7.114%   $46.7231   $46.72   $46.70   $46.70  
  7 purchase totals = $1,064.16       $1,165.1035   $1,165.10   $1,165.10   $1,165.00