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 $22.91   9.258%   $25.031   $25.03   $25.05   $25.00  
  Purchase #2 $160.37   9.855%   $176.1745   $176.17   $176.15   $176.20  
  Purchase #3 $11.58   7.715%   $12.4734   $12.47   $12.45   $12.50  
  Purchase #4 $101.95   4.261%   $106.2941   $106.29   $106.30   $106.30  
  Purchase #5 $146.53   10.834%   $162.4051   $162.41   $162.40   $162.40  
  Purchase #6 $30.71   11.475%   $34.234   $34.23   $34.25   $34.20  
  Purchase #7 $104.59   11.455%   $116.5708   $116.57   $116.55   $116.60  
  7 purchase totals = $578.64       $633.1829   $633.17   $633.15   $633.20