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 $209.40   11.549%   $233.5836   $233.58   $233.60   $233.60  
  Purchase #2 $161.50   8.788%   $175.6926   $175.69   $175.70   $175.70  
  Purchase #3 $119.62   6.829%   $127.7888   $127.79   $127.80   $127.80  
  Purchase #4 $20.58   8.128%   $22.2527   $22.25   $22.25   $22.30  
  Purchase #5 $236.74   6.434%   $251.9719   $251.97   $251.95   $252.00  
  Purchase #6 $173.86   9.503%   $190.3819   $190.38   $190.40   $190.40  
  Purchase #7 $215.40   8.558%   $233.8339   $233.83   $233.85   $233.80  
  7 purchase totals = $1,137.10       $1,235.5054   $1,235.49   $1,235.55   $1,235.60