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 $125.61   10.829%   $139.2123   $139.21   $139.20   $139.20  
  Purchase #2 $214.77   9.114%   $234.3441   $234.34   $234.35   $234.30  
  Purchase #3 $45.28   13.435%   $51.3634   $51.36   $51.35   $51.40  
  Purchase #4 $127.88   13.620%   $145.2973   $145.30   $145.30   $145.30  
  Purchase #5 $129.43   11.748%   $144.6354   $144.64   $144.65   $144.60  
  Purchase #6 $196.57   6.273%   $208.9008   $208.90   $208.90   $208.90  
  Purchase #7 $182.62   5.594%   $192.8358   $192.84   $192.85   $192.80  
  7 purchase totals = $1,022.16       $1,116.5891   $1,116.59   $1,116.60   $1,116.50