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 $63.94   8.278%   $69.233   $69.23   $69.25   $69.20  
  Purchase #2 $116.55   5.669%   $123.1572   $123.16   $123.15   $123.20  
  Purchase #3 $184.37   9.867%   $202.5618   $202.56   $202.55   $202.60  
  Purchase #4 $47.71   8.469%   $51.7506   $51.75   $51.75   $51.80  
  Purchase #5 $226.95   3.612%   $235.1474   $235.15   $235.15   $235.10  
  Purchase #6 $60.75   5.337%   $63.9922   $63.99   $64.00   $64.00  
  Purchase #7 $26.78   5.587%   $28.2762   $28.28   $28.30   $28.30  
  7 purchase totals = $727.05       $774.1184   $774.12   $774.15   $774.20