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 $65.91   5.612%   $69.6089   $69.61   $69.60   $69.60  
  Purchase #2 $169.29   10.656%   $187.3295   $187.33   $187.35   $187.30  
  Purchase #3 $173.55   3.565%   $179.7371   $179.74   $179.75   $179.70  
  Purchase #4 $51.32   11.149%   $57.0417   $57.04   $57.05   $57.00  
  Purchase #5 $162.28   8.382%   $175.8823   $175.88   $175.90   $175.90  
  Purchase #6 $104.93   11.638%   $117.1418   $117.14   $117.15   $117.10  
  Purchase #7 $214.31   8.608%   $232.7578   $232.76   $232.75   $232.80  
  7 purchase totals = $941.59       $1,019.4991   $1,019.50   $1,019.55   $1,019.40