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 $63.88   7.209%   $68.4851   $68.49   $68.50   $68.50  
  Purchase #2 $207.74   8.657%   $225.7241   $225.72   $225.70   $225.70  
  Purchase #3 $207.41   6.533%   $220.9601   $220.96   $220.95   $221.00  
  Purchase #4 $93.30   4.496%   $97.4948   $97.49   $97.50   $97.50  
  Purchase #5 $101.49   13.228%   $114.9151   $114.92   $114.90   $114.90  
  Purchase #6 $104.50   3.844%   $108.517   $108.52   $108.50   $108.50  
  Purchase #7 $168.44   6.670%   $179.6749   $179.67   $179.65   $179.70  
  7 purchase totals = $946.76       $1,015.7711   $1,015.77   $1,015.70   $1,015.80