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 $40.30   10.380%   $44.4831   $44.48   $44.50   $44.50  
  Purchase #2 $176.92   4.397%   $184.6992   $184.70   $184.70   $184.70  
  Purchase #3 $169.60   4.311%   $176.9115   $176.91   $176.90   $176.90  
  Purchase #4 $226.57   4.581%   $236.9492   $236.95   $236.95   $236.90  
  Purchase #5 $203.87   3.102%   $210.194   $210.19   $210.20   $210.20  
  Purchase #6 $42.65   4.631%   $44.6251   $44.63   $44.65   $44.60  
  Purchase #7 $82.25   6.520%   $87.6127   $87.61   $87.60   $87.60  
  7 purchase totals = $942.16       $985.4748   $985.47   $985.50   $985.40