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 $168.50   5.414%   $177.6226   $177.62   $177.60   $177.60  
  Purchase #2 $209.42   3.719%   $217.2083   $217.21   $217.20   $217.20  
  Purchase #3 $174.90   10.193%   $192.7276   $192.73   $192.75   $192.70  
  Purchase #4 $153.70   9.508%   $168.3138   $168.31   $168.30   $168.30  
  Purchase #5 $53.97   10.434%   $59.6012   $59.60   $59.60   $59.60  
  Purchase #6 $185.80   11.710%   $207.5572   $207.56   $207.55   $207.60  
  Purchase #7 $9.85   7.366%   $10.5756   $10.58   $10.60   $10.60  
  7 purchase totals = $956.14       $1,033.6063   $1,033.61   $1,033.60   $1,033.60