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 $192.93   7.329%   $207.0698   $207.07   $207.05   $207.10  
  Purchase #2 $154.64   5.418%   $163.0184   $163.02   $163.00   $163.00  
  Purchase #3 $49.65   8.630%   $53.9348   $53.93   $53.95   $53.90  
  Purchase #4 $73.25   5.736%   $77.4516   $77.45   $77.45   $77.50  
  Purchase #5 $160.43   12.777%   $180.9281   $180.93   $180.95   $180.90  
  Purchase #6 $248.49   7.563%   $267.2833   $267.28   $267.30   $267.30  
  Purchase #7 $118.72   12.155%   $133.1504   $133.15   $133.15   $133.20  
  7 purchase totals = $998.11       $1,082.8364   $1,082.83   $1,082.85   $1,082.90