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 $105.66   8.384%   $114.5185   $114.52   $114.50   $114.50  
  Purchase #2 $64.95   10.242%   $71.6022   $71.60   $71.60   $71.60  
  Purchase #3 $45.81   9.116%   $49.986   $49.99   $50.00   $50.00  
  Purchase #4 $222.32   11.708%   $248.3492   $248.35   $248.35   $248.30  
  Purchase #5 $17.43   6.485%   $18.5603   $18.56   $18.55   $18.60  
  Purchase #6 $154.36   12.647%   $173.8819   $173.88   $173.90   $173.90  
  Purchase #7 $242.58   5.444%   $255.7861   $255.79   $255.80   $255.80  
  7 purchase totals = $853.11       $932.6842   $932.69   $932.70   $932.70