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 $22.63   13.740%   $25.7394   $25.74   $25.75   $25.70  
  Purchase #2 $238.77   5.375%   $251.6039   $251.60   $251.60   $251.60  
  Purchase #3 $162.54   12.606%   $183.0298   $183.03   $183.05   $183.00  
  Purchase #4 $35.42   8.581%   $38.4594   $38.46   $38.45   $38.50  
  Purchase #5 $214.86   8.716%   $233.5872   $233.59   $233.60   $233.60  
  Purchase #6 $76.71   4.710%   $80.323   $80.32   $80.30   $80.30  
  Purchase #7 $214.53   8.783%   $233.3722   $233.37   $233.35   $233.40  
  7 purchase totals = $965.46       $1,046.1149   $1,046.11   $1,046.10   $1,046.10