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 $164.94   11.824%   $184.4425   $184.44   $184.45   $184.40  
  Purchase #2 $57.86   11.357%   $64.4312   $64.43   $64.45   $64.40  
  Purchase #3 $226.74   13.650%   $257.69   $257.69   $257.70   $257.70  
  Purchase #4 $87.76   8.870%   $95.5443   $95.54   $95.55   $95.50  
  Purchase #5 $180.28   11.271%   $200.5994   $200.60   $200.60   $200.60  
  Purchase #6 $170.85   7.605%   $183.8431   $183.84   $183.85   $183.80  
  Purchase #7 $249.83   13.103%   $282.5652   $282.57   $282.55   $282.60  
  7 purchase totals = $1,138.26       $1,269.1157   $1,269.11   $1,269.15   $1,269.00