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 $14.46   5.448%   $15.2478   $15.25   $15.25   $15.20  
  Purchase #2 $216.85   12.780%   $244.5634   $244.56   $244.55   $244.60  
  Purchase #3 $26.41   6.433%   $28.109   $28.11   $28.10   $28.10  
  Purchase #4 $116.76   13.639%   $132.6849   $132.68   $132.70   $132.70  
  Purchase #5 $177.28   9.370%   $193.8911   $193.89   $193.90   $193.90  
  Purchase #6 $176.44   11.346%   $196.4589   $196.46   $196.45   $196.50  
  Purchase #7 $53.68   7.205%   $57.5476   $57.55   $57.55   $57.50  
  7 purchase totals = $781.88       $868.5027   $868.50   $868.50   $868.50