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 $216.28   4.689%   $226.4214   $226.42   $226.40   $226.40  
  Purchase #2 $249.87   11.396%   $278.3452   $278.35   $278.35   $278.30  
  Purchase #3 $59.66   11.436%   $66.4827   $66.48   $66.50   $66.50  
  Purchase #4 $87.88   4.257%   $91.6211   $91.62   $91.60   $91.60  
  Purchase #5 $85.93   13.509%   $97.5383   $97.54   $97.55   $97.50  
  Purchase #6 $226.44   3.605%   $234.6032   $234.60   $234.60   $234.60  
  Purchase #7 $248.70   11.662%   $277.7034   $277.70   $277.70   $277.70  
  7 purchase totals = $1,174.76       $1,272.7153   $1,272.71   $1,272.70   $1,272.60