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 $25.99   9.325%   $28.4136   $28.41   $28.40   $28.40  
  Purchase #2 $74.60   4.713%   $78.1159   $78.12   $78.10   $78.10  
  Purchase #3 $153.87   9.654%   $168.7246   $168.72   $168.70   $168.70  
  Purchase #4 $149.66   3.348%   $154.6706   $154.67   $154.65   $154.70  
  Purchase #5 $82.54   6.177%   $87.6385   $87.64   $87.65   $87.60  
  Purchase #6 $52.40   11.441%   $58.3951   $58.40   $58.40   $58.40  
  Purchase #7 $114.62   12.390%   $128.8214   $128.82   $128.80   $128.80  
  7 purchase totals = $653.68       $704.7797   $704.78   $704.70   $704.70