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 $102.87   11.359%   $114.555   $114.56   $114.55   $114.60  
  Purchase #2 $49.94   12.746%   $56.3054   $56.31   $56.30   $56.30  
  Purchase #3 $148.62   8.433%   $161.1531   $161.15   $161.15   $161.20  
  Purchase #4 $176.81   7.313%   $189.7401   $189.74   $189.75   $189.70  
  Purchase #5 $202.26   13.252%   $229.0635   $229.06   $229.05   $229.10  
  Purchase #6 $107.37   8.498%   $116.4943   $116.49   $116.50   $116.50  
  Purchase #7 $162.73   7.275%   $174.5686   $174.57   $174.55   $174.60  
  7 purchase totals = $950.60       $1,041.8800   $1,041.88   $1,041.85   $1,042.00