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 $230.57   13.713%   $262.1881   $262.19   $262.20   $262.20  
  Purchase #2 $202.82   6.870%   $216.7537   $216.75   $216.75   $216.80  
  Purchase #3 $94.83   9.419%   $103.762   $103.76   $103.75   $103.80  
  Purchase #4 $152.72   3.291%   $157.746   $157.75   $157.75   $157.70  
  Purchase #5 $241.32   10.669%   $267.0664   $267.07   $267.05   $267.10  
  Purchase #6 $174.45   8.458%   $189.205   $189.21   $189.20   $189.20  
  Purchase #7 $230.28   13.352%   $261.027   $261.03   $261.05   $261.00  
  7 purchase totals = $1,326.99       $1,457.7482   $1,457.76   $1,457.75   $1,457.80