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 $153.80   13.244%   $174.1693   $174.17   $174.15   $174.20  
  Purchase #2 $207.36   12.235%   $232.7305   $232.73   $232.75   $232.70  
  Purchase #3 $107.25   6.620%   $114.35   $114.35   $114.35   $114.40  
  Purchase #4 $212.87   8.381%   $230.7106   $230.71   $230.70   $230.70  
  Purchase #5 $83.31   8.747%   $90.5971   $90.60   $90.60   $90.60  
  Purchase #6 $247.40   13.118%   $279.8539   $279.85   $279.85   $279.90  
  Purchase #7 $84.46   8.730%   $91.8334   $91.83   $91.85   $91.80  
  7 purchase totals = $1,096.45       $1,214.2448   $1,214.24   $1,214.25   $1,214.30