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 $47.44   13.111%   $53.6599   $53.66   $53.65   $53.70  
  Purchase #2 $210.87   7.451%   $226.5819   $226.58   $226.60   $226.60  
  Purchase #3 $223.84   5.872%   $236.9839   $236.98   $237.00   $237.00  
  Purchase #4 $241.93   10.469%   $267.2577   $267.26   $267.25   $267.30  
  Purchase #5 $182.82   5.521%   $192.9135   $192.91   $192.90   $192.90  
  Purchase #6 $106.90   7.513%   $114.9314   $114.93   $114.95   $114.90  
  Purchase #7 $5.89   7.592%   $6.3372   $6.34   $6.35   $6.30  
  7 purchase totals = $1,019.69       $1,098.6655   $1,098.66   $1,098.70   $1,098.70