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 $208.99   13.658%   $237.5339   $237.53   $237.55   $237.50  
  Purchase #2 $33.66   5.597%   $35.544   $35.54   $35.55   $35.50  
  Purchase #3 $31.60   11.114%   $35.112   $35.11   $35.10   $35.10  
  Purchase #4 $226.63   11.674%   $253.0868   $253.09   $253.10   $253.10  
  Purchase #5 $173.28   8.727%   $188.4021   $188.40   $188.40   $188.40  
  Purchase #6 $40.78   6.675%   $43.5021   $43.50   $43.50   $43.50  
  Purchase #7 $184.74   12.492%   $207.8177   $207.82   $207.80   $207.80  
  7 purchase totals = $899.68       $1,000.9986   $1,000.99   $1,001.00   $1,000.90